Reason you sometimes get slower speed with a booster is you lose MIMO capabilities of your device, as most booster don't support MIMO, still in a weak signal area non mimo speeds are still better than the latter.
Mimo stand for muliple in muliple out
Without mimo on your booster you are getting 1 better signal but just one, the device only got one copy of the data so if its degraded it must ask to resend thus slowing your speed, of course this all happens in milliseconds.
With mimo you are always getting two copies of the data, so even if the signal is more degraded your hotspot has two copies to look at, if one copy is missing a piece it can pull from the other and vice versa, only if both copies are bad does it have to ask to resend.
This is also why most hotspots have 2 antenna ports, so you don't disable mimo. This is a feature in almost all modern cellular devices, even the ZTE Mobley has MIMO as it has 2 internal antennas.
I learned about all this on the hofo forum.
