@antlestxp
"@dmbgo you want to be above 60 for the enclosure but not to high if printing small parts. Goal is to have the layer cool just enough to start to become solid but not enough that it shrinks."
To answer your last question first, yes, I did print 2 separate test cubes about 250mm apart, to see if the extra time for layers to "set" helped - it didn't, the issue remained unchanged.
I'm fairly sure now that it's not being caused by a shrinkage issue. I have, in the past, successfully printed objects in the same enclosure using ABS with similar settings.
in a day or so, I will try using PETG with its recommended settings to see if the issue is ABS, or happens with all mediums, as @fcwilt suggested.