Spitfire Gunsight adjustment?

[SEE]

I use my shoulder straps before pressing the trigger. I have noticed that weapons are more accurate/effective when 'strapped in' . It's a worthwhile observation you make as I read sometime ago (before CoD was released) that being 'unstrapped' would incurr penalty and now wondering if that also includes gunnery/accuracy of sights now that you have quoted the manual.