The 6'1" landlock is a LONG board. A typical skimboard like the Phase 5 Prop or Calibrated Pintail is in the 4'6" range a full 1.5 feet shorter. Going a little faster might lengthen the pocket and with that BIG 'OL board, you could probably ride in the 11 mph range.
Your rope length shouldn't affect where you're riding AFTER dropping the rope. If you need to get further back in the pocket, put the brakes on
Transfer weight to your rear leg, slowly and the board will drift back, then transfer weight to your front leg to mainatin that spot or head further forward.
If you're currently riding it doesn't sound like you need to make any changes to the wake, unless you just need to lengthen the pocket, see below. You might try to visualize where 18" down from the nose would be and see if having a shorter board would feel more comfortable.
You are right that at 130 pounds you could ride a much smaller board without problem.
It almost sounds like you have TOO much weight in the back - a steep wake with a short pocket length. Possibly speeding up to about 10mph if you are running slower than that. Also, if the wake is "pretty large" in comparison to some of the pictures you see here, transferring some of that ballast towards the bow might help lengthen the pocket and reduce the height of the wake. A picture of the wake would really help us, along with the deatils of your setup (ballast and speed setting).