I'm full time, but the safe harbor rules seem to be based on a 32-hour week for some reason.
I did look at your link, and I think you've read it right. I was calculating a $298 premium based on $40,000 salary, $3600 HSA deduction, and 9.83%, but the safe harbor drops it even lower to $256.
Again, I'm less interested in reporting them or losing my job over $.50/hour health insurance bump, than wondering if I should tell them or let them figure it out on their own. I think their other employees are young, so they're paying a reasonable age-rated premium.
I looked at the KFF calculator and it gives a $415 subsidy. My state insurance program lists only a subsidy of $290 at $40,000 salary, and I live in an expensive state so I don't understand the discrepancy.
ETA: If I read it right, and I may not, employer penalties only kick in if I decline employer coverage and take ACA coverage. I am unlikely to do so at my subsidy level. But, even if I did, the penalty for them is $338 per month, which is a lot MORE than paying the $80 difference to me, but it's a lot LESS than paying all of their employees another $80/month towards health insurance. If even half of the 60 employees take employer coverage, it's cheaper to pay the penalty for one person going off-plan.