I don't think that SS will be the only brewery/pubs that give "only" 95% liquid. There are plenty of pubs around here that give less than especially with Lager. If it's too big ask for a top up as the poster says. However, what is reasonable in my eyes may not be reasonable in someone else's. I don't mind a 5% head, in fact if I don't get that then to me it's not a good pint, but 5% is enough head.
I suppose this can be debated until the cow's come home and probably will.