Planet defense, mines, etc

[Beorne]

Two short questions on SEIV.

1) I have two ships defending a planet (with platforms, satellites, defending base etc). If I'm attacked on strategic battles the AI is so smart to keep the ships near the planet or send them away?. I think the latter, so how could I modify the ship strategy to keep them near the defending base?

2) I have no experience in removing minefields. Let's suppose I have to disarm a minefield of 30 mines. I have a minesweeper that can sweep 15 mines a turn. I suppose that if I drop the sweeper on that sector it sweeps all mines in 2 turns. But if it is in a fleet with other ships, what happens? The other ships blows up after a turn? And if I cross a minefield with a fleet containing a sweeper that has less sweep capacity than the field what happens?

Thanks