Took the JPlank 135 and supercruiser with 1300 front wing attached out yesterday in near perfect winter conditions. Managed about 75km from go to wo but the GPS battery died at 63km. It may not be perfectly matched but would the grin on my face been any bigger with a shorter narrower board. May be a little but not much.
Biggest problem ATM is availability and to many, affordability of a specific foil board. I have waited months for foil gear I have ordered in the past and now. Heaps of people are still using slalom, formula and free-ride boards and still having fun on them. Let's face it, far more foils than boards have been sold so far so it will be a while before most people are riding perfectly matched gear.
So if you have a JPlank and a free ride foil ignore the back straps and just have some fun on it.