This is an attempt to illustrate the difference between pinning the trigger in high and low positions.
The low position gives an easier install, commercial trig plate assemblies are available in this configuration. However, the angle between trigger pivot and and sear pivot increases the leverage required to trip the trigger. There is also a fair amount of SLIDING between trig bar and sear, which is another problem in that it requires force to overcome the sliding friction.
Higher position reduce both sliding friction and angle between trigger pivot and and sear pivot. This helps a lot. Also polish and case harden the trigger bar surface and polish the sear bar for slicker smoother operation.
This goes without saying that the sear nose and notch are in perfect geometrical relationship, and highly polished.