3 mines kill basic infantry so 4 should be enough now, except for $1000 characters. The trigger radius is about 50% lower than in Renegade but the damage is about 1.5 times higher and you can't hug the wall to take almost no damage from Proxy mines, unlike in Renegade.
Has anyone tried mining above the doors btw? I was playing around with writing a plugin for the Dragonade server side mod system for Renegade and I wrote a simple mod which lowers the vertical (Z-height) trigger range of Proximity mines, and this fixed mining above doors because the mines no longer trigger. I wonder if in Renegade X the mines still trigger if you mine above the door.