[@Innue]There aren't any problem with doing a little math. Hell, it's only a degree more difficult than adding or subtracting values.
The problem is with the indications.
Fixed point gains give us a nice and predictable system. Yours would be almost like a mess in this aspect.
It'd introduce complex strategies which may not discriminate against new players but in return would pretty much bane players who participated in more matches in the beginning. They'll be around the top and earn meager point amounts while a "newb" can technically catch up to them in two matches at worst.
It may keep motivating people but I strongly feel you haven't thought about the full implications of this system.