I personally don't like using heating matts. I perfer to keep the temp where the trays with cuts are, to right around 82-83. But you gotta do what you gotta do
But yes, get it it where those plugs feel luke warm.
I would say I shoot for about 1/4-1/3 up the plugs with when watering them, let them wick it up.
Here's a pick I just took. I got liquored yesterday so forgot to check on them last night. They are a little too dry this morning
Here's an empty tray with my water/very weak nute solution about half way up
I stick the tray with plugs in there until they all get dark. You can tell when they are all wet. Notice how the plug in the pic is almost completely wet. In 10 more seconds it was.
Those cuts were taken about 6 days ago. I'm pretty sure that was the first time I watered them. They are just starting to pop roots.
Oh yeah, don't spray the leaves, spray the underside of the dome if needed. The only time I need to do this is at first.