If I cause a decent amount more damage to the attackers, then I pretty much always stay. And I PAmail them to tell them, as I would rather keep my ships alive ofc, but if they land, it's their fault and they'll probably believe me in future. In fact, most of the time, people don't land on me twice if it's a game of chicken and I have the ships available.
Though it also depends on who's attacking me. If it's an enemy alliance I'll be more inclined to stay at home, as it will mean that my alliance will cause some extra damage to the value of the enemy alliance. If it's not hostile, I'm more likely to consider running. And there's the other tactical considerations over whether I need them in future etc.