You've got the published top pay points but yes there are a few pay point caps which can possibly be triggered if you stuff up, are unlucky/careless with your bidding/unambitious.....
With the caveat that the rules keep changing, pay scales are alll over the place and therefore I'm very open to correction the last time I looked any LHR based SFO, regardless of fleet, who doesn't bid for all available commands and as a result ends up remaining in the Right Hand seat stays frozen/capped at PP18.