With autothrust off, thrust levers on A320 (and I suspect on the other FBW airbi too) work as normal trust levers. However, autothrust operation is much different compared to Boieng's autothrottle. Airbus thrust levers don't move with power changes and while A/THR is working, their position sets limit to maximum N1 the A/THR can command. Normally they're set to CLB detent or MCT in one engine operation. N1 equivalent to current thrust levers position is displayed as small circles on N1 ECAM EWD display (upper center one).
So on airbus after you set the thrust levers to clb position, the autohrust is active and its control range is between climb power and idle. I don't claim this to be the answer to the original question, but it's the best that I can think of.