Gain is most likely the problem, reduce it.
The inverse cone above your antenna where it doesn’t receive well is very small at low altitudes so the small plane should be visible except for 3 seconds directly over the house.
Some explanation in regards to gain:
Thoughts on optimizing gain - #2 by wiedehopf
As for combining two receivers with the --net-only method mentioned above, i’ve written some scripting to make that easier:
GitHub - wiedehopf/combine1090: Combine data from multiple ADS-B receivers into one readsb decoder / tar1090 webinterface