I thought the efficiency of the front mount compared to the top mount is more defined under the high boost applications.
With high boost, the lag of a front mount is out weighed by the increase cooling efficiency and increase in power due to lower intake temps than what is achievable from a top mount.
Under low boost the difference in intake temp between the two types of coolers is less therefore the lag factor of a front mount can negate any power increase.
Thats my thoughts on the subject.