This attachment is a copy of Chuck Cunningham's article in RCModeler of many years ago.
A couple of things I've added after float flying for approx 25years

I put about 1/2" toe in to the front, it helps to track.
I make the spread about 1/4 to 1/3 of the of the wingspan.
The tip of the float is 2 1/2" in front of the prop.

Good luck

HughO