Hi Tom
Your "Sketch" is somewhat correct indeed, a low volume or narrower/thinner board that sits deeper, is easier to "hold" tilted when learning true.
The 3 strap thoughts are wrong though, as they are even easier to learn on (and hold tilted ready to start) than a 2 strap - but that is not the main issue here.
So yes, a narrower longer board will make initial learning easier when you are still struggling just getting up on the board, you are probably spot on
BUT, when you have learned for real, to ride with a bit of confidence, you will probably not like your current board at all anymore (except for "those were the times when I learned foiling" artifact that you can hang on the wall for its bests use), and the T40 or something similar will be WAY way better as a hydrofoil board
Glides easier, feels (and is) lighter and less swing weight, can be pumped to foiling in marginal wind much faster - simply everything is better, not in doubt.
You are at an extremely early period of learning, so yes, just like some use a shorter mast for some hours, then ditch it and go for a normal mast - you might do the very same regarding boards.
Why not keep your "perfect T40" so you can advance on this, as soon as you have learned?
I am waterstarting strapless on the T40, both with a heavy alufoil that sinks much faster, as well as with a lighter carbon foil - no problem at all starting strapless
Yes, you might not like the T40 later, nothing is 100 % sure, but have never read or heard about anyone not liking it - and have ridden it a lot myself now too (it is not mine, so easy to be objective) and can only confirm it is really good.
PF