unable to realign finger positions for BSI on iPhone

Thanks for that prompt response. When I started with BSI, it took me a long time to work out just how sensitive to tap speed the calibration process is, but I think I had that sorted out and that my problem isn't due to tap speed. I have persisted and eventually had success in screen away mode. The key to success appears to be ensuring that my fingers aren't too close to the middle of the screen. It feels as if this has changed and that the 3 finger groups now need to be further apart than before, but I guess that's just my memory fooling me. I'm having more trouble with table top mode. I'm only successful with calibration if I place my fingers almost parallel to to short edges of the phone and well away from the centre of the screen. I'm sure I used to be able to find a more comfortable position with my fingers closer to a diagonal position. Anyway, with your help, problem almost solved, but I'm puzzled by the change I think has occurred. Odd.

Thanks for the replies to this one. I am currently doing a lot of telephone support and training for iPhone users with sight loss and I don't have a spare iPhone, so I'm constantly making changes on my own iPhone to mirror work that the learner is doing at the other end of the phone line. I don't normally have Zoom enabled on my iPhone but I had turned it on during a remote support session. It eventually occurred to me that my BSI problems might be due to Zoom being enabled. They were! With Zoom enabled, BSI is nearly useless. It isn't possible to recalibrate the dots in the usual V formation in tabletop mode and screen away mode requires extremely uncomfortable finger positions near the edge of the screen. Turning off Zoom allowed me to recalibrate the finger positions just where I wanted them and I can now use BSI reliably again. Just one more VoiceOver feature that Zoom interferes with. What a relief! I was beginning to think that my Braille typing skills had seriously regressed. I can now resume my Braille training course and start working on my BSI typing speed.

Thanks for the information and I'm glad it works better for you than it does for me. It would be interesting to know what hardware and software version you are using, please. On my iPhone 8 running iOS 13.5.1, the effect of enabling Zoom is repeatable and disastrous for BSI. Not only does it make BSI typing erratic, it also impacts heavily on calibration. My guess about calibration is that the system gets confused by two three finger taps in rapid succession, as they need to be for calibration, and maybe interprets the two three finger taps as an attempt to turn on Zoom. I have found, and a previous post confirms, that calibration needs the left three finger tap to follow the right three finger tap at approximating the standard double tap speed.
Here are the symptoms I experience.
In table top mode:
If I look at my screen with a magnifier, I see that dots 1, 2 and 3 are marked diagonally closer to the screen left edge than I normally place my fingers. On the right, only dot 4 is showing, extremely close to the screen right edge. If I attempt to type with my normal finger positions, the results are wildly inaccurate.
I attempt to recalibrate and eventually succeed with my fingers in an uncomfortable position far too close to the screen edge and almost parallel to the short edges. The dot positions shown on screen are completely wrong.
Again, typing is inaccurate.
In screen away mode, things are generally a little better.
Again, if I need to recalibrate the dots, I have to hold my fingers uncomfortably close to the screen edges in a position that I find hard to maintain.
Sometimes this works reasonably well but my typing accuracy is reduced.

Now, if I disable Zoom:
In table top mode, I can now calibrate the dot positions in a V shape that is comfortable for me to maintain with my two index fingers near the screen centre bottom and my ring fingers near top edges. Also , the dots displayed on the screen are displayed in the correct positions. My typing is now accurate and reliable.
In screen away mode, I can now easily calibrate the dot positions in a comfortable position with my fingers closer to the centre of the screen and my typing is accurate.

So, for me, tabletop mode is virtually useless with Zoom enabled and screen away mode is more difficult to use.
With Zoom disabled, both modes work much better for me.

I suppose this may be due to an interaction with something else on my iPhone but it is definitely easy to provoke the misbehavious by enabling Zoom.

By the way, I found calibration difficult for ages until I realised that it requires two brief touches, first 3 fingers on the right then three fingers on the left, at about double tap speed. It's a pity that this isn't made clear in Apple's user guides!

I will report my experience to Apple Accessibility but I'd be interested to know if I'm alone in experiencing this.

Thanks. No problem. Actually that made me smile. I haven't yet got used to the Zoom conferencing service being so well known that it dominates Apple's accessibility feature. I also understand why you might think that there's no demand for the combination of the Zoom magnification feature and BSI, but there is. People like me who still have some useful sight and adequate hearing may not want to use a Braille display, but BSI, with a bit of practice, can be a lot faster than using the on-screen keyboard with VoiceOver. That's my objective. I also have the little Orion pocket sized Braille keyboard on pre-order which will be a lot easier to carry around than a full-sized bluetooth QWERTY keyboard when I want to do some serious typing away from home. Orion told me last month that it might start shipping at the end of June. It will be good to have a physical keyboard to use alongside BSI.
Thanks for taking time out to respond. It's appreciated.
Brian