One thing you have to remember about digital TV signal (aka OTA signals), even though there is a “signal strength indicator”, it is basically 100% on, or 100% off (aka the “digital cliff”). If the signal falls below the threshold to lock in the signal, you don’t receive the channel.
The signal strength indicator on the Tablo isn’t always accurate in my experience. I have both the quad and the original 4-tuner DVRs, and when compared to my TV (2012 Samsung 60" Plasma), they are virtually the same in performance (tuning of channels).
That being said, it took about a year to get it perfected. If you over amplify the signal, it can overload the Tablo’s tuners. If the signal is too weak, you won’t get a channel tuned in. And to make matters worse, atmospheric conditions can cause problems as well, not to mention that the TV stations have been in repack mode for a few years now, and ATSC 3.0 is on the horizon, which can put the stations on temporary lower power.
The Antenna Man recommends this tuner: https://www.amazon.com/dp/B07YLK76Q2/?ref=exp_antennaman_dp_vv_d
It will display the signal strength of stations, and make it easier to fine tune a station. Best results in my experience is having the signal strength between 80-90% for optimal performance for the Tablo DVRs.