Its important to stress that Rational is sus to me at this point, but he's still pretty much null from a non-vibe standpoint. His behavior fmpov cpuld reaaonably be coming from a town or scum. His pressure on those who are pressuring him, aka "omgus"("omg u suck") voting, is in line with his general behavior of retaliatory voting in response to people voting him.
His thematic post that was, at best, less than entirely relevant, could be a town player being overzealous with contributing show knowledge, even if that knowledge might not be totally relevant.
His paranoia of disclosing too much info to mafia by hypothesizing as to potential roles definite villain characters might be justified as having, though it doesn't make sense fmpov, is kind of in line with Rationals natural propensity towards such paranoia. Paranoia not to be taken in the negative sense, as townies should have a healthy dose of paranoia in acting.
This final point though, is what moves him into sus territory. Because as I pointed out, refusing to hypothesize only really benefits mafia, as they already know their roles. Being willing to acknowledge he could ultimately still be town, operating in a manner that is benefits exclusively scum, as illustrared by the final point, is more than sufficient reason for a claim.
Basically, the reason for claim is no longer exclusively him illustrating he is less than stellar at faking claims(beginners 1.2). We now have a sus behavior to back that up.