It'll work, but especially with the factory turbo, I wouldn't suggest it. The factory turbo spools quickly, but doesn't produce enough volume to quickly fill a FMIC and all the boost tubes. A basic rule of thumb is, you can run a TMIC on any turbo up to GT30 sized. Some builds even use a TMIC with a GT35 turbo, though the factory TMIC is replaced with a larger aftermarket unit. A FMIC will definitely increase turbo lag. If you're having knock issues, I'd look more into the tune and fueling than anything else. Also, on very hot days when you are sitting in traffic, try not to get on boost right away. Wait until you are moving down the road and have good air flow to the intercooler and throughout the engine bay before getting into boost. This should help you avoid knock from heat soak.
Look into a larger TMIC. Also consider different fuel types, if they are available to you. I don't know if you have E85 or something similar. Methanol (or water/methanol) injection keeps knock under control as well, though that adds complexity and the possibility of methanol system failure---which if that occurs---will likely destroy the engine.
Maybe talk to @
Alin and @
HolyCrapItsFast about the TMIC cooling fan mod. You could also do some exhaust wrapping, thermal reflective tape of the IC body, etc. to help control underhood temps.
All in all, I wouldn't go with a FMIC on the factory turbo or anything smaller than a 20g for that matter, but that's just me... If you do chose a FMIC and you have no plans to upgrade the turbo in the future, make sure you don't get a massive FMIC because that will only make the lag worse.
By the way, where are you located that temperatures reach 45*C? I lived in subtropical climates for a number of years while driving the Subie and while I sometimes noticed some insane underhood temperatures, I never ran into issues with knock and that was before my FMIC and methanol system.