I appreciate the reply. To be honest (dare I admit it here on APUG) I am printing with digital negs using Pictorico OHP Premium. The area shown in the attached pic was exposed through the Pictorico. I determine my exposure by the time at which additional exposure (through the OHP of course) will not yield additional print density. For example, with my current workflow I get increasing Dmax as I increase my exposure time to 3:30, exposing longer than 3:30 does not yield any increase in Dmax, so I set my exposure time to 3:30. I know this is somewhat of a departure from using a step wedge as some do, but the logic in it seems reasonable, no.
I have considered masking the negs in computer by simply creating a black border around the image area, and I haven't completely ruled out this option. Despite my conservative coating technique I would still really prefer to show the coated area outside of the image, thus I am hoping to resolve the issue.
I will give the mylar backing a shot. That combined with more rigorous humidification practices should at least make for a better print and hopefully help solve the issue.