First session yesterday on my new 6'10"x30"x125l "Simmons" board

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I have SUPed this same 6'10" board for some time now, and for me it is one of the stablest shape I used.
And after 35 sessions on my 8'9" foiled board, I felt I was quite OK foiling (nearly never missing a takeoff, controlling my flying height, pumping to keep & accelerate flying, connecting waves), but of course with still a lot of things to learn (how to pump for the takeoff, pumping on flat water, smoothly threading bottom rollers...)
But: mixing the two: 6'10" + foil... I didn't thought it would be so hard!
Not in the air, of course. 1' less at the nose and the tail, plus 1.5kg less total makes the board incredibly easier to lift out of the water and control in flight.
And actually, on waves steep enough to take off normally on a SUP, it was as easy as with my 8'9". But things were ... interesting ... otherwise. Weak waves were very hard to manage (granted the chop from 15knts onshore winds did not help)
I guess that on very short SUP boards, you develop a "3D balance" where you are moving your board around in all directions both to keep your balance and move around while paddling and takeoff phases (things that do not happen in prone surfing, the body in the water dampen things). But these movements, especially the rocking, will interfere badly with the foil dynamics, and vice-versa the foil forces will interfere greatly with a short board that will move more in response to foil forces. Trying to pump the foil would result in the board sinking vertical by the tail or nose, titanic style. Pumping in the air is simpler: you only have to manage the foil. Pumping on takeoff seems quite harder, as you have to manage both the board and the foil, and they react differently.
After 30mn I began to get a bit the hang of it, but there will be work. For now, on weak waves, I move a lot forward on the board (front foot near the front edge of the pad) to "choke" the foil and take off using the body movements I am used to for taking off with Short SUPs, and move to the straps once taking off is under way. And on steeper waves, I just take off feet ins straps as usual.
But this is not ideal, I guess now I have to learn to move the board on takeoff on weak waves so that the movements are beneficial both with the board and the foil. Back to the beginner stage!
And to people wanting to start SUP foiling: just like SUPing, do not start with too short a board! Granted my 6'10" is much nimbler in the air, but the technique is the same on my 8'9", only with slower reactions. So you can learn all the flying techniques as well on a longer board, no worries.
PS: I guess in understand now why foil-specific short SUP boards seem so thick. It may be to dampen the reactions of the board and let the foil do the talking...