Mind? No I live to talk about it, ******* obsessed.
What we are doing on this forum is known in the business world as "Brainstorming" and it can be very useful.
For instance, you have identified something I was doing, either accidentally, or subconsciously. (I prefer to think it was the latter) I now realise the importantance of this one small detail. The stone must be tilted.
I too was getting erratic results with the test model (I was using a capping stone from the garden wall) at the time I was only concerned with getting the stone to drop in the hole, I varied the height of the towers in relation to the bottom of the hole, with some success. However on the 4 ton stone (which is much more predictable in its movements) I used a piece of 4 by 3 across the balance piont which in effect tilted the stone, this tilt was increased as I placed the "A" frame under the stone. I now reckon both these facts are vital. The height from which the stone is dropped, in relation to its length and the depth of the hole, and the amount of tilt on the stone. On the plus side a stone of 10 ton should be even more predictable and so on.
I've only given it a quick thought be feel instinctively that raising the stone on a tower will be much quicker and more stable than building a ramp perhaps I'm just anti ramp. I will think on and am open persuasion.