Though I did actually increase the prop load, without any effect noticed.
"Increase the prop load" how? The general rule is that you want them run faster, and given that you want to hold the speed in check, that usually means that you have to reduce the diameter. The inside/outside problem is usually a matter of low gas velocity/internal ballistics, and we are running them at a tiny fraction of their capability. Anything you can do to get a less efficient prop increases the shaft power while maintaining the same airspeed/horsepower applied to the airframe (which are one and the same) is usually to the good. It also sucks fuel better - although I see you have an aftermarket venturi, which will make it more likely to run OK at low revs which exacerbates the inside/outside problem. Most of the successful 46SF runners around here used old 46VF props, like a 12-3.75 2-blades or 11.5-4 3-blades.
Note also that as far as flying goes, what is a "increased prop load" on the ground is not necessarily more in the air. A 12-5 is much more load than a 12-4 *on the ground* but not necessarily in the air. You might have to spin it 9500 in the air with a 12-5 and maybe 11,200 in the air with the 12-4, the drag on the blade is about the same, and you get a lot more power at 11,200 than 9500.
Brett
p.s. by the way, beware those DubBro filters. The black part is just pressed into the aluminum body, and they are notorious for leaking around that joint or just falling apart completely. I used them in the ancient past, but to be sure, you have to push the insert as far in as it can go (without blocking the outlet), peen the aluminum over it, then fill the bottom with epoxy.