I've been experimenting tonite with some different methods to try and "fix" this issue.
I tried adding and taking away washers, but that didn't help.
So I tried Feral's suggestion of manual line lay to pack out the centre of the spool.
this worked to a certain extent, but I found it hard to get an even distribution by hand.
Same theory, different material....I got out the electrical tape and used it to bulk out the spool, first with full tape width wraps, then with half tape width wraps, centered on the spool to create the right shape as below.
Using layer after layer of tape made keeping levels easier compared to working with the round profile of mono backing.
A bit of trial and error involved, but now my braid is sitting much neater and and runs off the spool much easier.
Looking forward to getting out and catching a fish on it now!
If anyone else is having this problem and has the time (like during a dust storm!) to go through this process, you might want to give it a go.
rocket