The filter supplied with the kit I last had was rated by K+N on a naturally aspirated car at 309 bhp. It was not a very big filter.
Even if you get a bigger filter in the space available I have not come across an inner wing installation that is not going to start being a restriction somewhere around 380-400 bhp.
The restriction posed by a filter is not like an on off switch. It is a progressive increase in pressure drop in the inlet tract. As the pressure drop increases the turbo has to work against the pressure drop to induce air to the compressor. This is easy to measure if you invest in Magnahelix guages and you will soon recognise that a smallish filter on a biggish turbo results in a big pressure drop. I cannot relate that exactly to power figures produced v pressure drop figures but an actual example of inlet tract improvement only (with remap) with a bigger filter and shorter tract length is going from 417 bhp to 451 bhp, same rollers, everything the same apart from induction and remap and all done within a fairly short period. The car was specifically mapped by the same mapper (Bob Rawle) for the APS CAK and then the new set up.
I would guess you could have a 500 bhp turbo doing 450 bhp because of the restriction of the filter or and another actual example, a 20G doing 345 bhp that went on to make 384 bhp.