Susan, is your probe one of those long pointy metal ones? If so, I'd go as low as you can so the angle of the probe is as shallow as possible. That way you'll have more of the tip buried in beans.
HC4U, my glass never gets cleaned. I gave up on it, as you can do it every ten roasts, and with an accurate temp probe you don't really have to see the beans. The crud doesn't build up all that thick, and eventually it'll start to flake off, at which time it can be scraped off easily.