Isn't the QAM reading what matters? I have Digital Preferred TV and BLAST internet. When my modem reads around -25dBmV - -17dBmV is when it has issues, and the channels on my cable boxes that seem to be lower than most other channels and seem to go out first are operating at 609MHz. they start tiling around -16dBmv.
On an average day, my modem reads around -18dBmV (the avarage, because my ARRIS modem has 4 different downstreams on different frequencies), and my TV Boxes from -12 to -19 (different channels/frequencies)
i don't think anything else matters besides what the modem and boxes read.
Here is my setup now:
line 1 > to Settop1
line 2 > to 2-way splitter > then from the 2 way, one to settop 2, the other to my modem
line 3 > settop3
im pretty sure 3 of the 4 inside lines are RG59 and one is RG6, i plan on replacing them all soon because i did math and for the approx distance for each ill save from 3dB - 8dB on each line.
and im going to eliminate the 2 way splitter, and use a 4 way outside so each device has its own line of the main splitter.