I know you probably know this but for any others who are learning...
The booster should be put at the point where the feed enters your house. This is where the signal will be at it's purest with least noise.
The longer the cable you add and the more splitters you add, the more noise is introduced into the signal. The SNR value is a display of the amount of signal that it can see over the noise. So if you have loads of noise, it will be hard to see a good signal hence the value goes down.
If you add the booster at the start, you will be amplifying more of the good signal and not a lot of noise. But if you add the booster after 20 feet of cable, you'll be amplifying the noise as well as the signal.
But, as you know, it's like a black art this cable hacking malarky lol!
If it works for your setup, you're a winner!
Also, if you have a good SNR %, i.e. 96% and also high BER then you could have a strong signal and an attenuator would be needed.