Start with the usual step for troushooting apps, especially helpful with rules in particular: enable all logging, and provide the output of those logs here.
Your rule looks like it should do what you said, so this will help figure what else must be going on. My guess is that it's not consistently staying under 1 W when idle or does so for more than one minute when not, but Logs will avoid this guessing.
You might also want to take a look at a rule I shared a while back that looks like it's what you're trying to do, sans the repeat (that would be easy to add; the difference here is how you're triggering and waiting for power):
