Thanks Steve but knew that anyway !
Tried board with a 32 (Drake; I think from a K 107)
Transformed board for use with 6.2.
IMO you can mess around all day but will never overcome inherent probs. On any board a 6.2 will require around a 32cm fin (or one corresponding to this ones area)
A specific sail area needs a specific fin to go with it.
Was worried how large I could go on US type box and if anyone with a K97 had found similar probs with standard fin !