Firstly, the strain screw places the pre-load on the leaf spring. As in any spring obeying Hooke's Law, it's reaction is only linear and predictable over a certain range. The strain screw is there to assist in removing/replacing said spring and should always be fully tightened. If you want a lighter DA pull - and the lighter primer whacks that develops - change that leaf to a Wolff reduced power leaf. As the only spring you work against in SA is the trigger rebound, you might have a revolver someone has clipped a few turns off of it's rebound spring, a Rube Goldberg approach at best (Again, that linear spring rate reaction...). The spring should be full length - just change the wound wire size for a different rate - again, Wolff reduced rate springs.
I'll wager you need a stronger rebound spring - you can demonstrate this simply by noting the small return force after you pull the trigger. For competition, or just rapid follow-ups, the OEM springs higher rate is actually a 'good thing', while the reduced DA effort after changing the hammer spring to a reduced power spring will likely tie you to the lighter effort Federal primers, not a problem here, as I make my ammo.
Also - recall that all springs 'wear' - take on a 'set' as some say. You must replace magazine springs - and recoil springs in SA's - you must recall that your revolver's springs may also eventually need replacement.
Stainz