Several words no answers
I can't see there being any perfect (or even near perfect) solution.
The combination of irregular clothing, irregular terrain and variable angles makes things so difficult to pin down. Marshalling in ISF events is predicated on the conformity of each and every shot; angles of limbs and such like can be used to regulate positions. Just as our shots are moveable feasts so are our positions; this makes for a very tough situation for both regulators and marshalls. I believe it is beyond the scope of reasonable expectation to hope that every shooter will be willing and able to consistently regulate every other shooter in every possible positional circumstance. An upshot of this is that even if general rules are accepted as fair there is no way they will be consistently applied.
As far as it goes, taking the seat right out of the equation has to be of some benift as making a call on when too much of the knee region is on the bag is just so vague. I would hate to have to marshall my shooting partners, I would hope to be there to share an enjoyable experience not rain on any parades. My personal concern is that people who shoot have a nice time. Life is not fair, neither is everything about FT.
My opinion, and it is only that, is that some latitude has to be expected of this position or it should be taken out of the course of fire in favour of more standers or perhaps reducers.
One option, if the position is to remain, might be that at least half of the supporting forearm's length should be past the knee. This would take the collapsed kneeling stance out of circulation and reduce the possibility of rifle fore ends touching the supporting fore arm and wrists touching knees. In practice this too would be difficult to enforce; just what point is half way down the forearm?
It's a bit of a mess. Removing the stance would place UK shooters at a potential disadvantage at international events but regulating the position is like juggling with gravy: highly unsatisfactory.
Whatever is considered should be weighed against regualtions in other countries. I think the sport is at a stage where rules should be converging toward some sort of global standard.
The best we can do as shooters might be to communicate with our BFTA reps, support their efforts and try to follow whatever rules might be passed as we can best understand them.
Love and kisses