Just to reinforce printbus' comments:

Reversing the airflow on the Hex HE is a big win.
Allowing significant build plate heat soak time, ditto.

The only persistent caveat I've encountered has been w/ the i3v 12"..., try to keep the objects centered on the bed and away from the edges, ESPECIALLY the front edge of the build table. Huge temp variability across the surface...

I still use ABS almost exclusively..., mostly because PLA goes brittle too quickly for my rate of usage.