What levels should I run to get the most heat??

I suspect it has to do more with the depth than the level, but I have noticed that arenas give out more heat... I have started at tier 3 and gone through arenas only to have hardly any heat given, meanwhile I do the arena right before jelly king and it gives me almost half a bar on a 4 star item around level 3-4. So is it affected by depth, party size, doing levels past the terminal?? Please leave your insight here...

Arenas on even numbered stratums (past basil). Resurrecting dead party members, etc.

Boss stratums.
Specifically, Jelly King stages. Simple and profitable. 5kcr a run, a full heat gauge per stage.

ask others to give u heat at arenas thats a good way to get some extra heat
also if u can do FSC it gives good heat

Please... Don't do Ironclaw Munitions Factory for heat. It gives very, very little.

Going to try and confirm some of these statements now.
I believe the amount of heat you get from least to greatest is this:
stratum1, 3, 2, 5, 4, 6