So I've got 2 anvils right next to each other. I went to combine two shovels recently (both Eff 4) and got different costs: one anvil wanted 13 levels to combine them, but the other one only cost 11. This isn't an order effect; neither anvil cared about which order the shovels were in. The only difference was which anvil I was using. The wiki doesn't say anything that would explain this, as far as I can see. Any ideas why this is happening?