My probe is about a 1/4". That seems like a very bump and will make it difficult to slide the tub I think. I don't see any pics in my searches of how people place their probes in a belly heat situation. I don't want to place it in a spare tub because that won't be available for very long. I want to use every tub. I don't foresee a problem with the probe being in a groove in the shelf but sometimes more experienced people have run into situations I haven't thought of.