I don't ride with straight arms.

As for the seat, if I scoot it back any more, I get the "pushing pedals forwards instead of down" sensation, and it gets harder to spin fast.

BTW, my seat (like most seats) has a slight sag in the middle. So I have the seat overall pointed up a little so that the rear portion is kind of level. If I tilt it down any more, I get the sensation that my saddle is pushing me forwards. If I tilt it up any more, it's hard to lean forwards without crushing my nuts. (especially if I do the "rotate hips forwards to flatten the back" thing)