Yes indeed, I mentioned that a lot of the tactical options are only available if the defender has at least 2 minute warning on missiles, which is a good deal.
Anything big enough to detect them at that range is going to be an enormous target. But if all the defenders need is warning, not targeting, maybe a huge line of buoys with resolution 1 active sensors could work. That would be a lot of magazine space, even if the buoys are cheap, and it would need to be something you could automate, because doing 100+ waypoints by hand would be ridiculous.
Also, the buoys would have to have enough reach to see a fast missile crossing its sensor reach, which would mean you need a lot of overlap.
For buoy design, you can apparently get ridiculous duration if you get a .1 msp missile drive with max fuel efficiency.
Still, if you are designing a trap for a higher tech (spoiler), and have the time to prepare and know the approximate vector the (spoiler) is going to approach the warp point, a buoy early warning net might work, while being hard to detect until the enemy got within its own AMM range. And vs (spoilers), if you can get them to waste their ammo on buoys, GREAT!
Normally, I would argue for one big sensor, as a sensor 10x as big would cover 10x the range, so 10 little sensors in a line would only cover 60 degrees of arc. But if you want your sensor ships to be able to withdraw as well from a big wave, while still have info about other incoming waves, that is a problem. If you have high confidence about the vector the AI is coming in on, a 20 degree arc might be sufficient for tactical advantage. If you are roleplaying a race that has a high sensitivity to casualties in offensive operations, especially vs (spoilers) that have ripped apart a fleet or two, might be a fun approach.
IF you can come up with a minelaying missile deployment technique that doesn't drive you bonkers. Getting a buoy that can detect missiles across a 5 second flight time might be too big to be usefully deployed, however. I would do some designs, but Aurora is currently borked, possibly because there is something wrong with my computer, or several things. 5-seconds would be enough for a warning system, as the buoy line would at least detect missiles moving past it, if there were decent overlap.