But to my ears...
Fire = Treble voicing switch, I use the middle as it feels most "vintage Plexi" to me
Tight = Cuts the low end, super helpful for cleaner tones (but can't say I do that much lol)
UFO = Diode compression, I forget which direction I use but it's the "louder" one which is no diodes I think (or maybe just "less")
Blood = Gain boost, I actually use it off most of the time but do flick it on from time to time
Storm = Most confusing to me but basically makes the low end louder without changing gain? I don't know but I use it in the middle with my tele and the other two settings with humbuckers
Input: I like the Low one the best but mostly because I use my SK for mid-gain