You didn't say whether the antenna is installed outdoors or in an attic....which may be
attenuating VHF signals more than UHF....outdoors is best....
I found RCA ANT-751 (aka EZHD) to be very difficult to model, esp the SWR....but from
what I see in the simplified VHF only modelling, it provides 2-3 dBi Gain on Ch2-6 with
only a bit more Gain in the Forward direction as toward Reverse. However, SWR is
climbing to ever more excessive levels the lower in frequency you go.....so adding first
6-ft, then 10-ft of extra cable length MIGHT help Ch2 reception...or NOT as the location
of the SWR Null is hopefully moved from being on the END of the coax....
If you have to receive Ch2, you might want to try a Combo antenna with better Ch2 Gain,
which unfortunately are rather HUGE. Alternatively, you might want to consider adding
a Ch2-6 Antenna, such as Antennacraft Y-5-2-6, with a HLSJ Lo-VHF/Hi-VHF+UHF
If you're in a DIY mood and have the VERTICAL space for them, you might consider
one of nikiml's Ch2-13 GHn Grey-Hoverman Antennas with a UVSJ UHF/VHF Combiner: