I remember from high school something called "The Scientific Method". Only change one variable at a time.
If you have an unproven plane, it would be prudent to use a proven float design.

I usually post a link to Randy Linderman's website when somebody asks about float design, but I already gave you that.
Here's another link with Ed Westwood's article from Model Airplane News. Ed Westwood also designed the BEAST from RnZ models, and RnZ also sells John Sullivan floats which are widely regarded as good. Round on top, flat bottom.

http://users.rcn.com/llfc/floats/