Swedish Mauser: FSR-type target sling adjustment?

I've just bought a great 1944 Husqvarna M96. It with came with what I always think of as the typical FSR leather sling - i.e. not either the common military version (although it does use the same brass studs to attach to the swivels) or the M41B version with the rubber anti-friction pads, although it does have two adjustable brass buckles similar to that design.

Question: is there a procedure for adjusting this type of sling to fit the shooter, I'm 5'9" with long arms and the sling is currently way too loose for me, but I can't see where there's enough adjustment to take up the slack or how the various elements should be placed when it's correctly adjusted?