Experimenting with this now @10 and 20NL, myself. Incorporating the 2.5x has been working out well over just a small sample but I don't even know why. I know from my own perspective, I don't like seeing it from the blinds b/c it almost forces me to feel like I have to call with more marginal holdings and ...yeah, I'm finding myself in spots where the blinds are calling me more liberally. It's also difficult to 3b size properly against it without almost giving the open raiser great odds to call IP. Sticking with 2.5x from LP and 3x from EP now. If I have one limper, 3.5x. Of course, this is just the beginning of me incorporating this with any understanding of it at all.

I like your question, though because CO is the line for me between 2.5 and 3x, also.

I see some people use 2.5x instead and I would like to use that.

Don't like that logic. Can check your winrate from CO and compare to MP/BU if have decent sample.

Can definitely raise for 2,5x but don't go less than that at microstakes. Pros for 2,5x that we risking less in case bu is good player or blinds are aggressive. Cons if blinds are weak players, raising bigger sizing superior

In general, as you open a wider range, you want to size down. 28% seems a bit too wide from CO for 3x sizing. I would prefer 2.5x with a 28% range (as a default).

If you have a decent sample, you can experiment with various sizes and see what works best.

The normal caveats about BTN being a nit, short stacks, weaker players, aggro players and tight players in the blinds apply.

Jesus Christ - 100k hands from each position. LOL

Like .00001% of the pop is going to do that.