its more about inlet charge temperature than power..
there is heat generated by the turbo spinning and heat generated by the compression of air and how hard the turbo is working...
say you were running a small turbo on very high boost, it would produce very hot air, because of the compression..and so the intercooler would have to work hard to dissapate the heat.
conversely if you ran a great massive turbo on lower boost once spinning it would pump just as much air and the temperature would be lower.. so the intercooler would have an easier time.
the top mount is well designed but suffers from heat soak when stationary..
an ARC top mount flows even better..
some front mounts have very poor end tank design that creates turbulance and drag, loosing you horse power.. others are of better design but have long pipe runs..