Hi

How much backing line do you spool on beneath the fly line please .?

I want to spool up my new [Greys Platinum #6 Dual Inter/Floating] line
onto a spare spool of my Greys GRX #7 reel
Backing is Greys 'Greylon (bright pink) 20lb braided

How much backing would you wind on normally .?
Should I add extra as it is a #6 line going onto a #7 spool .?

Many thanks in advance, regards