On residential I would use 80/50 tip between 60-80 psi
Ideally you want the spray wand to feel like if you let go of it, it would stay right where it was. It wouldnt drop or jump. Basically when you turn the wand on, its just floats in the air and you guide it back and forth. If that makes sense.
Trails come from:
Too low a pressure on a big tip
Too high a pressure on a small tip.
Sounds contradicting but its how it works out.
Playing around with it you will get it dialed in.
Once in a while If I jump on the spray wand, I use an 80/70 and run 85-90 psi.
Thats a little on the heavy side for pressure, but Im covering large areas.
Remember to change the tip often. Especially if you use sand. You;ll see that the spray pattern starts getting a little more round. You want a flat fan.
Buy your tips online. You should be able to get them for $5.00 or less and change them out often. You will really see a difference. Personally, I cant stand spraying with a tip thats not new. I change them more often than you need to, but it makes a difference.