Hi John K,
I'd suggest placing the mast foot fairly far back.
To get planing in really marginal conditions, you need to get the nose of the board UP to get the necessary for and aft trim to allow the board to jump up over it's own bow wave.
On a true 100 cm wide formula board, placing the mast foot near the back helps with early planing, but creates issues with high speed control once you get up to speed in fully powered conditions and heading downwind probably alot deeper than you (as a recreational sailor) would normally ever go.
You may be able to fin a larger or more powerful fin to get more fin lift sooner (in marginal conditions) to get you planing and keep you planing. The downside is if the wind comes up significantly, you would need to use a smaller fin to regain some control, and the larger fin may limit your top speed slightly.
Again, marginal conditions require special rigs/fins/techniques.
I would use a flat rail to rail triim to get planing, and if you are fully planing, you can use a little bit of
lee rail down trim to head upwind, but be careful as in really marginal conditions, heading very far upwind can drop you back off plane.
Try to get going on a reach or slightly below.
If you head upwind at all, while trying to get your board planing, you will actually diminish the likelyhood that you will plane.
Also, a couple of big pumps on your 11.0 m2 rig should help pop your board onto a plane. If it takes more than 2-3 pumps, chances are there's simply not enough wind.
If your board starts to plane, you can "pump the fin" with your back foot, once you are in the staps, to
help free up your board and increase your speed.
Pumping the fin simply consists of pushing hard (jabbing really) across the top of the board with your back foot.
A wider board would help, but you are already at 94 cms, which should be nearly as good as a full 100 cm wide formula board, but easier to sail and control in powered up sailing.
Hope this helps,