Is there a formula or chart that specifies what lowpass filter LAME will automatically invoke for certain bitrates? I've looked around the net and can't find anything on this.
And is there a specific logic that dictates said formula or chart, besides just listening tests?

--preset insaneseems to be using a lowpass filter as well... see http://sound.stackexchange.com/questions/38109/lame-why-is-a-lowpass-filter-used-with-preset-insane – Tieme Jan 24 '16 at 15:49