I can't seem to replicate this. The sense 2 shader doesn't appear to be affected by picmip at all for me. So my guess is that it is a combination of some other setting on your end as well.
However, when you start modifying your own settings to such an extreme degree, the algorithms that choose how to compress a texture might end up doing things that make it invisible by landing/averaging to a near black pixel. There is only so much control we have over that.