I am not sure whether you have mixed up the SD channels' signal strength with the perceived poor quality because they are SD instead of HD.
Please do a manual scan for the following channels and record the Signal Strength/Picture Quality using matv:
Chan 27
Chan 29
Chan 31
Chan 33
This will enable us to see if there is anything wrong with the matv.
Chan 27 issues de....poor signal strength/pic quality....the rest all ok with the MATV...avg around 65-70% strength and 50-60% quality