RE: isonic 111 - trouble with back foot
Poor guy. Our answers are pointing to different directions, and I guess are adding confusion to confusion.
Matt is such a big guy that probably the 111 + 7.8 combo is a 20 knots + setup for him. This could partly explain the use of smallish fins on such a big board. Nevertheless, at 200 cm and 100 kg, leverage power is such that it must be very easy to push too hard on the fin, expecially if one is seeking balance to sail railed.
Probably sailing style and stance are not to be overlooked. My guess is that the 111 (which I don't own or ride) could prefer to be sailed level, instead of railed. Maybe this does not show up in lighter winds but could be an instance at higher speeds (7.8). I do also think that with the mast forward one gets too much leverage which could be difficult to manage, while mast back requires more attention sheeting in but also does not lean towards excessive push on the fin.
Maybe someone who knows could make suggestions about the 111 character, if it is supposed to be sailed railed or flat. But beware: 2 meters tall + 100kg+ fast materials + correct stance + good setup... ind the end we could be generating a monster...