Nah, I'm stuffed
. I don't actually know the physics of it - just that too high is as bad as too low, which is why excessive shortening of your cable can cause issues just as excessive lengthening can. However, there is a tolerable range so unless it's already on the fringe before you start, it should be ok.
I came across an old schematic for a cable TV system once, the principle of balancing power levels seems to go into the complete design of the system from street cab to all serviced homes, with customers further from the cab being placed on higher taps inside the cabinet, which deliver more power to compensate for the longer cable run.