It does visually reduce AIP. Look at the tooltip for the AIP meter. It will have a value called AIP reduction. That will continue going up as long as you hold it. Also, there is a nice equation that explains the effective AIP.
Floor = Base AIP*0.2
AIP = Base AIP-Reduction, Unless AIP-Reduction < Florr, In which case AIp = Floor
This means that the AIP reduction is not wasted. If you have surpluss AIP reduction, it will be *used* to reduce the rate of AIP increase by 80%.