Thanks for the reply, and sorry for the delay...

Masquerade correctly defects against TemptingCooperateBot, for the following reasons:

• PA proves "FB(TCB)=TCB(FB)=C"
• PA+5 proves "TCB(DB)=C" and of course PA proves "DB(TCB)=D"
• PA+5 proves "TCB(Masquerade)=C" (though this is actually irrelevant, as Masquerade will defect at this point whether the sanity check succeeds or fails)

It's not that there's anything magical about PA+4 in Masquerade; my mental image is that Masquerade uses a large value for N, so that it has time to find mutual cooperation with all but the very loopiest of opponents. If you delay it until PA+4, then it'll just start from there, more or less.