There's a nice hot spot for the Logan system on I-93 south as you climb the hill after Furnace Brook Parkway. I'd also expect to hear it if you are near the Marriott off of Congress Street.
Maybe hospital hill as well, since it has good elevation.
The Commonwealth 700Mhz overlay shouldn't, at least in theory, have any MSP traffic on it.
Speaking of the overlay, coverage seems to be improving south of Boston.