Clashing with a yonko crew will somehow effect it, trust me. Plus I'm thinking that oda is trying to keep sanjis bounty under the other rookies since he didn't include him with them (despite sanji being stronger than most of them)
Sanji has always been the invisible man. He should be a nova but he isn't. He should have the third highest bounty but he doesn't. He should have an accurate wanted poster but he doesn't. He should have a last name a home town a.d parents but he doesn't.
Sanji has always used his low key status to hi advantage saving the crew countless times, skpiea when we thought he was ko'ed, alabasta when he was Mr Prince,Ennis lobby where he vanished and closed the doors. Almost ever arc sanji uses his invisible man powers (his anonymity and lack of title) to save the crew. Even now sanji vanished to fight a yonko.
Let his bounty stay low. Its his super power