How much convex (sides) is too much?

[Tom183]

I'm building my first boards this week, flat/finless 3/8" baltic birch. I already have one that someone else built for me but it has a very rectangular outline and tends to catch in chop. So I'm building two new boards, one with the same tips but wider in the middle for earlier planing, and another board that is shorter and about 2cm narrower at the tips with 2cm more width in the middle.

Q: how much convex is too much? I have compared to a production board and they're both pretty close, but we're talking plywood with flex and no rocker or fins, and I was wondering if a straight (or even concave) shape might be needed in a ply board?