No, the float doesn't >>Have<< to extend in front of the prop. It really helps with docking as the float nose acts as a bumper. Otherwise, as long as the float keeps the prop out of the water it will work. Last time we met, I had just slapped some old floats on my plane and they did not extend past the prop.

All the "rules" about mounting floats are not chiseled in granite, but in silly putty. Everything is a tradeoff.

Look up "Watts Linkage". It may be a useful trick up your sleeve with what you're doing.