Ian has given you the basics, but I have some questions.
When you are sailing fast, in the footstraps, with your rig raked back "all the way" what is your focus.....
1/ To get the foot of the sail down on the deck of the board.... (i.e. "closing the gap)?
2/ To rake the sail back until it balances over the fin (this is adjustable by moving the mast foot)?
3/ To get the foot of the sail parallel with the deck of the board (regardless of the amount of gap width) ....(i.e. raking the sail back to it's designed foot angle)?
Another question..... how much beyond the clew does your boom extend?
Is the foot of the sail dragging in the water, or the end of the boom?
I agree with Ian here.
Either the Ram F8 sails are cut with a very low foot angle or you are over raking the rig for some reason.
How much up off the deck is your sail being rigged.
Often, sailors don't rig the tack of the sail low enough, and in order to "close the gap" or bring the foot angle parallel to the deck of the board, they tend to over compensate for the higher than normal tack by racking the sail back more than the design foot angle.
As a general rule, with most modern sails, the front of the luff sleeve at the junction of the sleeve and the foot of the sail (some sails are "cut away" in this area so you have to project a straight line down from the front of the luff sleeve and forward from the foot angle of the sail) needs to be at or below the mast base where it connects to the UJ.
Take a look at this link:
The photo of Bjorn Dunkerbeck in the center of the page shows a fairly large Ram F8 rig at speed.
Notice how the foot angle is nearly parallel with the board in this photo, but also notice that the foot of the sail has a secondary clearance angle right at the back to prevent the rear of the foot of the sail from dragging/catching on the chop.
Is your sail somehow different?
If your sail has the clearance angle, then for some reason you are drastically over raking your rig to get the end of the boom in the water or your boom is somehow quite a bit longer than the normal clew length of the sail.
I've sailed a bunch of Isonics (all of them > than 101 liters), with a wide variety of Sailworks and Severne sails and like Ian, I've never had a problem with the boom end being anywhere near dragging in the water.
Even when I do my Bruce Peterson imitation and rake the rig back until the foot of the sail rolls a bit from heavy contact with the deck, the back part of the foot sometimes touches the water, but the boom end is still well clear.
Something about what you are describing as the reason you sold the 2006 Isonic 100 is not making very much sense to me.
Hope this helps,