Avoiding a drug because of it's scheduled status makes a lot of sense, and because of what it might be cut with, but I am not sure why someone, or how someone would cut LSD with fentanyl given how small I thought the effective dose of LSD is comparatively and how different the effects are.

Without gc/ms you just don't know what's in your tab/liquid/etc. That being said iirc it takes milligrams to OD on fent which means you'd be pretty safe with tabs. Liquid is another story.

[REDACTED] acquired LSD tartrate, made solution w/ everclear, and then diluted it such that one sip is roughly 4-8ug based on volume. That's the only real way to microdose yourself, although you could cut a tab into 20 pieces (depends on the lay but a skilled lay is evenly distributed. An unskilled lay will have massive hotspots and thus one would need to dissolve the tab in a solvent or cut it into n->infty pieces)

Buy a testing kit off of Amazon. You should be doing that always anyway.