When a UE is going to engage concurrently in a first transmission on a first channel and a second transmission on a second channel, the UE will apply a level of power-backoff for the first transmission, with the level of power-backoff being dynamically established (i) based on a prediction of what PSD-limited frequency in the nearest IM3 product will have the highest PSD and (ii) based on a mapping between that predicted worst-case frequency to an associated power-backoff value. For instance, considering the IM3 product nearest in frequency to the first transmission, a determination could be made as to what portion of the IM3 product is subject to a PSD limit. And a prediction could be made as to what frequency within that frequency range will have the highest PSD. That predicted worst-case frequency could then be mapped to an associated power-backoff value, and the UE could be configured accordingly.