Joe,
If you're combining a UHF antenna with a VHF antenna, use a UVSJ. It greatly simplifies the installation and the subsequent customer experience. There's no need for a two-cable run and an A-B switch in this configuration. There is no benefit to the more complex configuration.
Ken,
Location, location, location.
If the antenna is installed in what amounts to a dead spot for one or more channels, it won't work. It's very common, especially when behind trees or other obstructions like buildings, for such dead spots to occur. The recommended course of action is to try multiple locations using only temporary mounts. Find a spot where it works before you break out the drill, don't use the drill until that sweet spot is located.
Trees directly in the signal path cause me to simply throw all predictions out the window. Once cannot expect or estimate the extent (or lack thereof) of their impact on the incoming signals.
The selection of a small LPDA antenna such as yours should be completely appropriate given your TVFool plot. However, I can't figure out from the obtuse descriptions whether you simply have an indoor amplifier or if it's split power supply/inserter and remote amplifier configuration. If it's a simple indoor amplifier, placing at a single TV set is probably too late as there's very little it can do to improve reception. Based on your plot, an amplifier would be ill-advised anyway due to the calculated strong signals. However, remember my comment about the trees...
According to 1ByOne's response to a question on it's Amazon listing "the antenna has built-in amplifier, and the white box on the picture is power supply box." I have the power supply at the LR TV. Product webpage here: https://www.1byone.com/TV-Accessorie...nna/OUS00-0550
You didn't identify the make and model of your TV set that you used to compile the chart, but I can assume that the readings in the rightmost columns are of the SNR values posted by the tuner and are not actual power levels.
Yes, they are SNR values. TV is a 2012 Samsung LN 40D630M3F.
be aware these readings are not an accurate indication of received signal power, they're an indication of how much above the signal floor the signal is. Generally, a SNR of around 15 dB (+/-1) is required for decoding. Increases in the SNR improve your margin to dropout (reception failure). SNR readings will top out in the mid 30s regardless of what you do. Due to the effects of AGC and other digital magic, the change in the SNR will NOT be perfectly linear across the range of the displayed values. FWIW, if you can get the SNR into the low 20s, you usually have sufficient fade margin for the majority of situations. However, when those trees are wet and the wind is blowing, you can almost expect reception failure, so do keep your expectations in check. Think of the nursery rhyme about Humpty Dumpty...
If you want to try a preamp that you can pick up locally, Home Depot stores carries the Winegard LNA200. While I'm not a fan of it, I note it as a utility device that just happens to be available almost anywhere. Assuming your existing amp is simply an indoor amp (put it off to the side), the LNA200 can be installed at the antenna, and the power supply inserter at either TV set (your splitter is diode-steered and will pass power though it to the amp). If it isn't an indoor amp that you have, then never mind.
Good luck!