It took me more time than it should to understand that last point from some of your previous posts on the same subject but I now understand you are correct in that getting that weight up high ought to help balance the machine.
I had the same with Paul's post where he mentioned that a higer seat does not work on Alan's design.
But it all has to do with speed and amount of tilt.
With a 2 wheeler, you will tilt less ad low speed in a corner. But with Alan's design, you need to tilt ad a surten angle and it doesn't mater how fast or slow you go, that angle is set.
So speed decides how hard it is to ho back upright and don't drop further.
With a higher seat, you will hang more to the inside, so with low speeds, you will get the falling effect.
With a low seat, you will hang over way less.
The wheels is an other thing. Bigger wheels need to tilt more, to get the same turning circle as a smaller wheel. This will make that your speed needs to be higher than with a smaller wheel.
Probably he used the mount in the middle from the lower booms, to set it up in the amount of tilt he needed to steer. That is probably why he could move it forward and backwards.
I am not surten, but something you can play with to see what got effect it has.
Tilt and steering are linked, but by linking the tilt to the steering and not to the speed, it makes that you need to tide ad a minimum speed to go trough corners. The faster you go, the bigger and higher seat you can mount. As you hi slow, lower and smaller wheels are better. Overall smaller and lower is better, even with higher speeds. It is a trike to ho fast with and nog slow.