Uh... 50% what now?
Is that saying half of the, lets just say 3" for now, half of the 3" round area should be blade sweep, which is just determining the hub/pod/spinner size,
or half of the sweep area should be blade... kinda like 1/2 the prop disk should be prop.
Imagine the fan is a disc of paper with no blades cut out to start with. The disc would be divided into 8 and then half of the pieces are cut out to leave four blades with 1/2 the blade area.
The hub area is relatively small even at 40mm, which is a good size to hide most of an engine in.
I didn`t mention diameters, I have used 75mm (3" ) and it seems just right. I think you could go smaller to say 2.5" or 2.2" if you made a drive shaft to get the engine back from the fan and motor fairing ala C/L speed plane, AND used an engine happy to run 35K like the GZ/ Cyclon / Fora
But then as fun as it would be, you would want to be pretty motivated when 3" works pretty well.
J.M