I think the most efficient way to lay mines is to use fighters or LACs with box launchers.
You can either use 3-stage mines, or deploy them as buoys. And you can make fairly big mines that you can nonetheless deploy relatively rapidly.
I am a bit torn about the best size for mines. The larger the mine, the better sensors you can have, the longer the range it can engage at. But the larger it is, the more easily it can be detected in turn, and potentially taken out before it can launch.
So what range do mines need? Their most notable use is as warp point interdiction. So they need enough range to cover against the enemy jump engine range, and possibly a TL up from that.
But if you are using fighters to deploy or 3-stage mines, you can deploy them in unexpected places, in the path of an expected enemy movement. And for that you need a much larger range.
I could see mines being used as a forward defense of a warp point, where they are used to thicken the medium ranged firepower of the defense, before beam range. The theory being that the defense will use point defense against long ranged bombardment, will duck out through the warp point if there is a truly large missile wave, trusting to fighters staying behind on the warp point to whittle through the loitering missiles, while the mines make it hazardous for the attackers to move in while the defending fleet is on the other side of the warp point.
Actually, if defenders continually cycle part of their fleet through the warp point, they are likely to cause long range missile bombardments to lose lock outside of the range of their onboard sensors. They still go to their target's last location, but if that was offset from the warp point, the myopic sensors on the missiles might not be able to reacquire.