As a BA silver you must fly more than me but my upgrade rate, over I suspect significantly fewer flights, is far better than that as a blue, both from WT and WT+, as is the OP's by the sounds of it.

What routes do you take and what frequency do you fly each alliance? Also what class do you normally fly, as if you're mainly in CW, you're obviously far less likely to be OPUP'd than if you were in WT/ WT+