There are many things that make throat-irritations, but the throat-hit, atleast to me, is specifically reffering to the thump effect of the nic upon reaching your throat.
About pg and throat-hit, then pg dosen't give throat-hit, but just dosen't mute it like vg, and just lets it through unadulted. Vg mutes the throat-hit, but the more water added to it, the lesser that muting effect occurs, e.g. adding 20% water practically dosent mute it anymore, so that's good for people wanting throat-hit without using pg.
I'm guessing it's because vg has a much higher boiling point than pg, so with vg then not as much liquid, including nic, is evaporated at a time, and giving off that throat-hit effect, than as if using pg. However, water strongly reduces that boiling point of vg and infact can easilly make it under that of pg itself. Maybe instead it has to do with the viscosity, and so the lesser viscosity, the lesser muting effect, I dunno, but nonetheless, it's noticable that water helps in bringing that throat-hit better forward, like that of the effect of pg...
As Kurt previously stated, then 20% water can be a bit to much in the higher wattage ranges, and I also agree with that. I myself normally only run at max 30 watts, and most often between 18-25w, so not much of an issue there, allthough on e.g. the subtank mini, then lesser water is probably called for even at "normal" wattages, since that atty to me gets really warm quick. I don't know if it's the smaller chamber or what, but e.g. running 20w on my lemo 1 and 2's, are an entirelly other feeling than running that same 20w on the subtank mini, and it gets really hot and crackles like crazy with higher water amounts. That's mainly the reason I preffer the lemo 1 and 2, and use them much more than the subtank mini(or the 'plus' version), besides the flavor too me is better in the lemo's. The lemo 2 brings a sweeter vape, and the lemo 1 gives a more deeper tobacco vape, both on the same unflavored 80/20 vg/water 3mg mix
I'm guessing it's because of airflow differences, as one is more open than the other, and I use both wide open...