Hi Danny L,
Guess I should not try to answer forum technical questions before my first cup of coffee in the morning.
I'm going to leave what I wrote above, but for your Severne sails, with the pulley that runs across the sail (vice fore and aft like the NP, Gaastra, Sailworks, and Windwings) it's incorrect.
The NP base that I have would seem to work perfectly with an across the rig tack pulley.
The recommended Streamlined "Quick 6" base pulley and cleat system works better with fore and aft aligned tack pulley sheaves.
Where ever possible try to get the mast base pulley system that avoids the "crossed axis" situation.
Then you can simply start at one side and "wrap" the line in each sheave progressively "across" the axle from the tie off point across to the cleat and everything lines up. If you have a 3 sheave tack pulley and a 4 sheave base pulley/cleat assembly, run the line from the tie off point under the first sheave on the LH side of the base so there is less "spreading" force on the tack pulley and the sheaves all line up better both at the top and the bottom.
So, for your NP base (which one....how many sheaves..?) start at the tie off point and run the line up and over the LH sheave in the tack block from the front to the back.
Then run the line down and under the LH most sheave in the mast base from the back to the front.
Then run the line up and over the middle tack pulley from front to back.
Then down and under the RH pulley in your base, from back to front, then up and over the last RH sheave in the tack block from front to back and then down to the cleat.
With parallel axis pulley "axles" you simply wrap your lines "across" the sheaves, starting at one side finishing up in the cleat on the other side.
Sorry for the confusion!