Minor fluctuations are gonna happen especially with a CHE. If you want to really dial it in, a lot of people use proportional thermostats, like the ones from Spyder Robotics (who come highly recommend from other users here). Those types of thermostats will change out much power they're pushing to your heating elements depending on how much heat is needed to get back to your preset temperature.
Something like what I use, and what you're probably using, is a simple on/off thermostat. The issue I've noticed using those with a CHE, is it takes awhile for a CHE to warm up, and then by the time it gets hot enough to trigger your thermostat to shut off, the bulb itself still stays pretty hot for awhile after. That's probably, if I had to guess, why you're seeing the minor fluctuations.
You just have to remember that these guys come from a place where the temp varies depending on where they are. I think a degree or two either way, +/-, from where you want to be is fine. I've had to learn to trust my snake to move to where he needs to be to be comfortable.