DougEfresh of the 2 20k guys that hit me at 10k, I bet one of them would have taken the odds and hit it. I mean shoot, one of them pulled a Full Send on me, pretty ballsy. Kicked my ass, but it cost them. If it only deters half of BFers, and you only lose castles on half the hits, that'd be pretty good progress on BFers imo.
If we found it restricted target pool too badly we could always loosen it a bit, maybe set the castle chance to kick in at 70%, or increase the odds to 60 or 70% in favor of the attacker. Dial it in so BFs aren't so prevalent, and players don't feel hopeless, but also not restrict the target pool too badly.