I track it and just lump it into TT in out of habit, but in reality it's really more like MU or an added cost since claim size is determined independent of whatever excavator you use since the numbers are set before you ever start pulling. It's just not a significant cost unless you're using something less efficient than TT exc., adj, or imp though.
"Best case" scenario for someone thinking it is related to TT returns is maybe that MA decided to add in a baseline amount in "additional" claim size to somewhat account for average excavator decay. That doesn't mean the particular excavator you use will affect your claim size (just probes+amp decay+finder decay factor into that), but just that a constant value of a pec or two might be added on after those other inputs are factored in.
I somewhat doubt MA would go to the work of that example, and it's not really worth the effort to test, but given the way things work in what we can see, that would seem to be the closest we could get to some sort of excavator factor in whatever formula is used to determine claim size. I'd honestly just bet that MA just has their figures on what probes+amp decay+finder decay = average TT% is regardless of what "extra" costs are to miners like extracting. They might just ignore that cost in what they set as average TT. If they're nice, maybe they bump up average TT% a little to account for excavators across all accounts, or maybe they just pocket all the decay. The example above is another option, but I really feel like we're in rounding error territory at that point from a game developer standpoint.
