Centre of gravity, flaps and elevators

So, my understanding is that as a general rule in flying, the further aft the centre of gravity, the less drag.
This is because as the centre of gravity moves further ahead of the centre of lift, the higher the torque that must be counteracted by the horizontal stabilizer generating downforce. If you can move the centre of gravity to the same place as the centre of lift, your horizontal stabilizer would not be producing a downforce - less drag (more unstable, more dangerous etc etc let's keep this on topic)

Something I've been struggling to understand is how the optimum centre of gravity moves when you add flaps and elevators to the mix.

Q1) I understand that negative flaps reduce the amount of torque generated by the difference between centre of lift and centre of gravity, but I'm not quite sure how - I assume the centre of lift has to move forwards because I don't see how the centre of gravity would change. Surprisingly there seems to be very little information about this on the internet.

Q2) My next puzzle comes from flying my unflapped glider aft, usually 90% aft. This means that when I am at cruising speed, I need substantial forward stick/elevator deflection to maintain that speed.

This doesn't feel efficient - so my question is, is it more or less efficient than if I had the centre of gravity forward such that neutral elevator produced my intended cruise speed?
Does further aft always mean less drag when you consider the elevator is required to maintain your cruise speed?