: I'm getting ready to build a SOF using Chris Cunningham's book.
: Maybe ...

: Also, is there any harm in building a slightly more relaxed fit to
: the kayak?

I'll let you know soon! I am almost finished with a SOF build myself, which is a Yost style frame but my own design. I am sizing it so that it is a relaxed but close fit. Meaning that I imagine myself being able to paddle it with bent knees if I wish but still have contact with the masik for rolling. We'll see if that happens in practice or not - so far it looks like possible in dry-land fitting.

Second, I already have a narrow tippy boat. I can do anything I want in it, but it takes more energy to paddle in rough conditions than a slightly less stable boat. I can go "forever" in the more stable boat while I tire in the less stable - it is like surf-ski: unless in the perfect downwind conditions, there is no amount of practice that will let you balance without wasting some energy on balance - it is just too tippy and requires part of the stroke dedicated to balance in side chop and confused seas. It takes years to get fully comfortable in a boat like that and will still be less than 100% in rough stuff. I did not want that in my new boat so I'm designing it a little more stable than the super fast boat I have but still quite lean by sea kayak standards for my size...