Is this what you have now?
Code:
C4 75° magn
264° magn \ H
CH 7 yagi UVSJ > preamp > coax > power inserter > TV
WCIQ \ / L
splitter
WGTV /
CH 8 yagi
78° magn
If it is, how does CH 7 do if you remove the splitter and connect the CH 7 yagi directly to the UVSJ?
Connecting two similar antennas, aimed in different directions, doesn't always work. The same signals from each antenna might interfere with each other if they are not in phase when they reach the combiner. Equal length lines are required for identical antennas aimed in the same direction. Equal length lines are irrelevant when they are not aimed in the same direction.