How much IIR to get uniques?

Been farming Piety and Dominus for a few hours now with 460 IIR or 420 if I dont shield swap in time and havent gotten a single Unique. Am I not running with enough Item Rarity? I see videos of people getting double or even triple drops with similar stats so dont know what Im doing wrong.

Yeah, that's RNG, you most certainly have enough item rarity. Few hours is too short, farm for a few days, it'll balance out.

there is also a big item quantity difference between playing solo or in full group (usually with dedicated MF culler)

I dont stack IIR at all, and farm piety, and on average find what I consider, a decent amount of uniques. RNG is a fuckin biatch.

I find uniques fairly often with 270-300 ish iir and 25 quant.
However i never find those useful ones. :P

Remember that if you stack to much iir you get dimishing return. And to be honest i feel 270-300 or so with some iiq is the sweet spot.
Also when you stack enough iir, iiq becomes more important/valuable than pure iir.

There's a good reddit post that explains the iir vs iiq ratio.