Amazing! thank you so much!

you are a hero to mankind, blessed by the god-emperor, thank you so much

Glad to hear, it is probably always best to just look for 1 more person and go in a private game

I tried to do this legit and half-legit many, many times. But this one place actually made it possible.
Done it seconds before I got kicked.

@Sofa King just tried the spot and it worked like a charm, though popup wasn't immidiate.

my 29 lvl Psyker sends his best regards

Thank you. I finished the achievement first try with help from your guide.

Another area that I figure it should be easy to complete this (haven't leveled Psyker yet but when I do I intend to try it) is on the Investigation mission (Hab Dreyko). After completing the finale event and you're doing the escape sequence, right past the triple catwalks that the Valkyrie partially destroys there's a door spawner right against a cliff ledge. Enemies are guaranteed to begin spawning from this door once you cross the catwalks so simply run up to it, wait until a big group has come out, then push. Should work really easily (haven't tested).

it did end up working; game just didn't pop up with it being completed.

Thanks for this tip mate, worked perfectly!