Just to check it out, I put on 'XLO on Comm. Ave. near BU, and it sounded HORRIBLE there. It was all multipath distortion.
The boosters are directional. The Hancock Tower booster is nulled to the west toward BU, so though it was only a couple of miles away, I was getting an attenuated nulled signal from it. The Lexington and Waltham ones are directional toward the east or southeast, toward BU and Boston, so I may have also been hearing one or both of them, then there's also the parent signal from Leominster, that is still fairly strong by BU.
I may have been hearing three or four signals fighting it out as I was driving down the road, though they had the same program, causing severe multipath with each other. It also sounded like one of the signals was overmodulating, adding to the distortion. Though I've heard the translators sound good in some areas, it was a real mess there.