The factor on its own makes it symmetrical but the deflection of the propwash vector makes it asymmetrical... Plus you also have a sideslip for the wings anyway, so its not symmetric even without propwash. But the "how much of the wing is affected by propwash" is fixed, doesn't change due to sideslip or angle of attack yet.
Well, here's a nice chance for further improvement of your FDM
It would also bring interesting effects for rotaries, now that they're coming along so nicely
Getting my mind prepared to hover in the R-22.....