I wouldn't be surprised if you have at least 10 db of loss in your coax run using
RG6 coax at these frequencies. To prove it, take the mobely up on the roof and hook to the short piece of coax supplied with the yagi. I would be willing to double down on my 10 db loss prediction and it may be more. Also of some small consideration is the "impedance bump" and resulting extra loss due to mismatch between the probably 50 ohm design impedance of the yagi and the 75 ohm characteristic impedance of the RG6 coax.
The good news is it worked. It would have probably worked better with some LMR 400 or some superflex or some other larger more expensive coax. Of course there is the law of diminishing returns, that is how much money are you willing to put in to the installation vs the return of a better signal. Good coax ain't cheap, nor the connectors for it.
Coax Attenuation Chart
By the way a 10db loss in a run of coax is significant. It is a logarithmic scale, but in this case 10 db of loss can be understood in this way. If used for transmitting, if you put 10 watts of power in one end you get 1 watt of power out the other end. Or if used for receiving, you get 1/10 of the signal out the bottom as the antenna puts in to the top end. Yes that is a significant amount.
