Logic...
With both engines operative, if you move one T/L above CL detent it becomes a manual T/L, and that engine will supply the selected thrust - it is progressive all the way to TOGA.
FCOM 1.22.30 p70 (look at the MAN THR line) ... says A/THR is armed and MAN THR will be displayed in White, unless the most advanced T/L is in the MCT or TOGA detent (MAN MCT or MAN TOGA in white). Logically the other engine will supply CL thrust since A/THR is only armed not active.
Logically yours..
TP