Yep front mount intercooler = full removal of FRS airbox as pipework on both items is not compatible with one another (airbox blocks the front mount cooler to inlet pipework)

TBH if your car is the one i think it is (focus with FRS lump dropped in it) there are only 2 options for air filter location

1st which is standard on all FRS running Gen II, PiperX, etc is pointing down next to the passenger side wing/wheel lining up in front of the fog light on the FRS bumper - no reason for heatsoak to be an issue with this setup as filter is down in the wing away from engine

2nd is to get some custom pipework done & locate the filter behind the passenger side headlight & run some cooling pipework from (well remove) the passenger side foglight - have a look on Cochyn's posts/pics of his current Focus RS to get an idea of look of that setup - again with good ducting/cooling i dont see a problem with heatsoak