This is not my first rig, but I was always satisfied with the automatic weights, but now I need manually place the weights.
I can’t upload the file, sorry.
Notes:
-I use the Empty groups option at the moment of apply the armature.
-The group showed in the screenshot, is the uny group that have values (try to eliminate other not resolve the problem).
Vertex weights are relative, not absolute, so if a vertex has a non-zero weight for only one group, that bone will drive it 100%. If you want only 5% effect, you need at least one other bone weighted to take the remaining 95%.