As it is not possible to scale the projection symbol directly and by defining it as a user defined symbol there will be no associativity between the symbol and the actual projection method used in sheet. However, by using the drafting attribute '<W@$SH_SHEET_PROJECTION_ANGLE>' as a user defined symbol, it will be possible to maintain the associativity.
This is a kind of workaround, check to what extent it is suitable to fulfill your purpose. The steps involved are:
I have shown the same steps in the following video. Hope it helps!