Sounds like you've got a slightly better sample than me
IIRC I had to go to 1.15V to get 1900IF to run. I frankly didn't make that much of an effort with my tuning - there are definitely some voltages I should have googled, among other things - but the cooler affecting things makes sense. The cooler I'm using now is a modded old Arctic Accelero S1 passive GPU cooler with a custom mounting bracket
I could definitely have fit a better cooler if I wanted to (my case could fit an NH-L12s or Big Shuriken 3), but none of those are likely to work as well passively as this does - I've set my fan to turn on at 60 degrees, which means the PC is entirely fanless unless I'm pushing it
I'll probably get a bit more into tuning it at some point down the line, but it needs to be 100% stable, so I likely won't be messing that much with it.