Actually the opposite. R/C carbs are not set up for crankcase pressure, and at anything but WOT the mixture gets totally messed up. Muffler pressure is far less in comparion, and gives only a very light amount of pressure. It may be that with a tiny orifice in the crankcase or backplate tap you "might" get okay throttling, but everything I've run into that addresses this subject says crankcase pressure is for venturis only. On larger engines I suppose you could use a Cline or equivalent demand regulator at the fuel inlet and take advantage of crankcase pressure, but since those weigh an ounce themselves they hardly apply to 1/2A applications.

On my VA .049 the muffler pressure tap is somewhere around #78-#80 drill, and that's just muffler pressure being moderated there.