I'm learning Heimerdinger and wondering how to understand his passive:

"Techmaturgical Repair Bots
Heimerdinger gives nearby allied turrets and champions 10/15/20/25 health regen per 5."

When does the higher number apply? When I reach a certain level? When I've been next to people for a long time? Or does it depend on my stats, such as HP or AP?

Sivir has a similarly confusing passive. It would be nice to know how these increases over time apply generally to any champs who have them.

It depends on a level, so at level 1 I get 10 regen per 5, at 6 I get 15 regen per 5 etc. (not actual numbers, but that's the idea)

Does anybody know at which levels these numbers change?

I think it's on levels 1/6/11/18, but it could be slightly different. Something along those lines.

probably 1/6/11/16, the same level you are able to level your ultimate. this is the pattern i have noticed with most scaling passives