Jay, when I back cut from that side, I basically keep my left hand on the side of the handlebar, which puts it on top of the powerhead since the saw is on it's side.
When I back cut from the other side, my left hand is on the top of the bar, so it is off to the rear of the powerhead when the saw is oriented to cut. I use 3/4 wrap handles so I could put my left hand on the upper side, but that feels like my arms are crossed over each other, with less accurate control.
Changing where my left hand grips the handle seems to keep my right hand in good position to operate the throttle. Neither feel awkward to me.