you saved my time, I was just going to apply this cure to 2.2. thanks.Beyond that, there's no core_fa.less file any more. It's been replaced with a pre-compiled fa.css template, so changes would need to be applied to that. (Note that this also pre-minified.)
This change was primarily to speed up core CSS compilation (and significantly reduce the memory overhead of it).
this might give an idea lol. i think the graph starts dipping around the same time when i moved to 2.2. i was running shrunk font files on 2.1. i am a bit confused about the instructions to follow for 2.2 so haven't dabbled yet.