Due to age-related diminishing flexibility I'm inclined to go with a larger cockpit on the Outer Island I've just started, similar to the cockpit of the Arctic Tern I built several years ago. According to Jay Babina's comment above that means I need to raise the cockpit. Looking at the sketch on the OI cockpit template, showing the kayak, the paddler and all of the forms it appears to me that I'll need to raise six of the forms, both to provide knee room and to avoid creating a huge curve in the cockpit coaming profile. The larger cockpit will extend forward of form 8, not to form 9 as with the original design's ocean cockpit. If I'm right, here are the changes I'll need to make to the affected forms:

F6, +1/4"; F7, +1/2"; F8, +3/4"; F9, +1"; F10, +1/2"; F10.5, +1/4". Expert OI builders - am I right, or what should be done differently?

I built an OI, but with the 'Ocean' style cockpit as Jay designed, so I cannot give you any exact advice.
A couple of comments based on other projects I've done:

-Did you draw the lines of the deck elevation (profile) out full-size, using a batten (wood strip) to get your measurements for modification? Doing a bit of old-fashioned lofting can help a lot, and doesn't take much time.
Taking some measurements from another kayak - sit in the boat and put some masking tape where your knees hit the deck, then measure from the seat back - can give you a clear idea of where you want the max deck height to be in your OI. Working toward deck 'bubbles' (like the NDK Pilgrim) to give extra knee room away from the center line is one idea, though a bit difficult to do with wood strips. If you can get 'up close' to some good glass boats, you can get some more examples. A flexible drafting rule and a piece of cardboard can be handy when stealing ideas.
The 'fit' is so important that I wouldn't hesitate to spend a few extra days getting it right, though you are probably eager to 'get going' with forms and wood strips.
-I'd consider using a 'keyhole' style cockpit opening (I like the NDK - style (Romany, etc)) which can give you enough room to tuck your feet into the boat while still keeping some of the knee-brace area under the deck. Another cockpit style (from my 'fleet' here ... ;-) ) that works well is the Mariner. A Google search for images can often turn up examples if you can't find what you want at the manufacturer website. A copy center can 'blow up' your image to a working size for a few dollars.

Please keep us posted as your project progresses!