Yep, that aiming issue is curious. That's why in these situations most of the experienced players prefer bots for gunners as they have no such problem while firing. In fact, sometimes almost everything depends on the elevation of the terrain.
I suppose this is some small part of the game mechanics which has not yet been improved.
As for the:
TheWhitestOfFangs wrote:
Also - is there a way to aim the turret towards a point without using the LMB (and accidentally shooting sometimes?)
There is no other way to aim afaik. But to avoid accidental firing while rotating the turret just aim farther/a bit aside than you want to stop the turret(main cursor as you said).
