I'm a bit confused... You say you are in Milford, NH. Your TV Fool report is for a location between Concorde, MA & Acton, MA.
Combining signals from two antennas that operate in the same band(s) (UHF, High-VHF or Low VHF) is not really an exercise in level matching or balancing. You would need an effective filter that allows desirable primary path signals from each antenna, while also blocking reflected path signals from entering the combiner. Without filtering, two high performance antennas combined will interfere with each other, leaving with less reliable reception.
Channel Master used to offer such a product, the 'Jointenna' which was a filter network. It had an input for an 'all channel antenna' and another input port for a single channel antenna. It would pass all but the one channel through the main antenna port and pass only the lone channel through the single channel antenna port. A third port on the Jointenna was the combined output. These were consumer grade devises and the filters had rather wide 'skirts', so you would see one or more channels on either side of the single channel blocked or reduced.
tinlee.com produces a variety of filters, including products similar to the Jointenna. They sell to the public but their prices reflect the higher quality and custom choices that they offer.
Here are a couple of other possible solutions to consider:
http://forum.tvfool.com/showthread.php?t=820
http://forum.tvfool.com/showthread.php?t=2882