It HAS to have been a man who came up with the idea that humping is dominance
Mia does it to Ben when play has got a bit hyper

Other dogs try and do it to Ben because he is a neutered male and apparently smells a bit like a lady dog (they do the teeth chittering thing) Ben is a v submissive dog to other dogs so if this was a dom thing then he wouldnt be chasing them away

I would be more worried about the head over back thing as well - but again it has to be taken in context looking at the body laungage of the two dogs and what happens before and after - and the feeling you get - if its tense then break them up

I was always told a dog standing over another dog is them being dom - but watching Mia with Ben it deff isnt

with her it is totaly a pain in the backside attention seeking behaviour 'look at me I am flashing my bits in your face, notice meeee play with meeeee'

this happens at the kennels all the time, i dont tend to worry about it but do keep an eye on dogs that are doing it