Right now I am running some fairly long coax cable when running my frequency measurements. I initially had about 100ft and i dropped it down to a 50ft cable and that helped a bit. Would I see better results if the cable was 30 or 20 ft long? I really only need about 15ft to go from my room to the dish.

If you reduce the receive cable length below 50ft you are unlikely to see any change in receive signal to noise ratio.  The wanted signal and the noise floor will both increase by equal amounts.

If you do shorten a cable consider cutting the outdoor end which is the more likely to have degraded or corrosed due to moisture.  Before cutting a cable make sure you have a new F connector and correct crimp tool tool and self amalgamating tape.  Axial crimp F connectors are excellent, but need special crimp tool to close. The tip of the centre pin should be smoothly rounded and stick out 1.5mm proud of the rim.  The outer braid must make good contact and no fragments of wire braid should be left to short circuit the DC power.  Use a magnifing glass if necessary.

Do not alter the transmit cable length without consulting your service provider, as they will have to adjust the modem transmit output level.  If this is not done, the service will degrade or fail.  Too high transmit level into the BUC is worse than too low transmit level into the BUC.

Best regards, Eric.