Heh, I wouldn't sweat it too much, Eli. Look at
the directional antenna pattern WELH proposed; it's extremely goofy. If Bob Surette at Shively told me otherwise, I'd listen to him...but based on my own experience, that pattern cannot be created without using expensive panel antennas, and even then it'll be a challenge to make 85% of the pattern.
I've seen a lot of applications like these (and done one or two myself)...an existing station files a last-minute minor change app right before the pre-window freeze last October. Maybe they'll actually build it, maybe they won't...but what they really want to do is make sure some new interloper doesn't shoehorn their way in on the existing stations' fringe coverage. It's smart strategy...in at least one of my cases, after the window closed there were suddenly a half-dozen new applicants on the existing station's frequency - and because I maximized their facility all those interlopers were shoved an extra thirty miles further away than they would've been otherwise, thus preserving fringe coverage over a nearby metro area.
FWIW, they are increasing height and ERP, but the DA pattern reduces most of that ERP heading northward by 70%. The end result looks like only 350-400 watts heading towards Boston...that's about 3dB more than they're sending now; not a big change. I imagine you'd see some nibbling to WMBR's coverage but not much; the hills near RT.128 serve as a terrain shield for WMBR (and WZBC vs. WRIU, for that matter) moreso than anything else.
You can always contract a guy like myself (well, technically I'm part of
Broadcast Signal Lab) to do a check and make sure there's no contour overlap but I suspect you'll just spend money to learn that WMBR has no grounds to object.
:-\ Them's the breaks, though...we all have known for years (decades, even) that the Boston dial was crowded and only going to get moreso, and that any fringe coverage just cannot be counted on. Just ask WZBC how they feel about WSMA! :'(
Barman's cousin must have an exceptionally good radio and antenna to pick up WMBR all the way down by the Cape. If he's right on the water, perhaps he's getting the benefit of some over-water path (there shouldn't really be one, the azimuths are wrong, but one never knows).