Need suggestions

Need suggestions

As the title states, I need suggestions. I have a print that calls for a specific groove width, at the bottom of tapered walls. Normally I would measure a cylinder, then two cones for the walls, create a two circles at the intersections of the cylinder and cones, then report the distance between the two. My issue is how short the tapered walls are. I'm guessing I could get in there with a very small probe, but I am wondering if anyone has any other suggestions. I've attached a snippet of a model that I made, I can't show the whole print on this one.