From what I have observed, it is for the top spot kind of thing or a way to establish pack order. All of mine are fixed. This is the order I got my dogs. Misty, Tannor, Robyn, Midnite, Brennan, Batman. Now follow this...Misty never gets humped and every now and then she will go for Tannor. Tannor will try every now and then with Robyn. Robyn never never humps anyone. Midnite goes for Tannor. Brennan goes for Tannor. Batman goes for Midnite. The pack order from what I can tell is Misty, then Robyn(she bumped Tannor and he tries to reclaim). I'm still deciding where the boys are because they all seem to be trying to get to Tannors spot. Midnite is really persistent about it. I think the order I got the boys still stands, it's the girl that bumped ahead. They stop when I catch them and yell. Did you understand all that?
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD