I've noticed some beans, via naked portafilter, pull very evenly almost every single time. As in, I have to really screw up for it to not pull evenly. And I've noticed others, like my current Intelly Tres Santos Colombian, pull evenly 10-20% of the time. It's not a taste issue because the beans that rarely pull evenly still taste good. It's more a curiosity and I haven't been able to dig up much information on the subject.

Is it a moisture % or roast level factor? Country of origin?

My setup is a Super Jolly and an Andreja Premium, with both stock baskets and VST baskets. Tamper is the Cafelat VST tamper.

I know roast level is a factor. I have pulled med - dark roast flawlessly and when I switch to a light roast I assume because dryer coffee when tamped doesn't compact as easy pulls through a lot faster. So when I switch to a light roast I tamp harder.