You need enough tension on the trigger"s mainspring to kick the rear trigger up with enough force to fire the lock. When you tighten the screw that retains the mainspring, this increases the strike of the trigger on the sear bar. But it also raises the working arm of the trigger so that it will eventually interfere with the sear. There is a fine line between where it will and won't work. One tune for that is to file the heel where the mainspring bears against the back of the set trigger until it floats without any tension on it from the mainspring. For this to occur, the mainspring must rest on the trigger plate while under the tension of the screw. then when you set the trigger, the mainspring bears on the trigger, lifting the mainspring. But having filed metal away from the trigger's heel, the rear trigger can now float again, dropping it's forward working end so that it doesn't touch the sear bar. This will take care of the set trigger/sear relationship.
But the front trigger also has to have enough metal removed so that when the rear trigger is pulled, which causes the firing trigger to rotate and it's lever touches the sear arm, there is clearance. It sounds like you're almost there.