hard to say for sure, but the general wisdom seems to be that:
- the losing team has to be the team that controlled the zone(s) last
- the winning team does not have a majority of ink coverage on two-zone maps (very unsure of this, but it might be the reason why sometimes taking one point is enough to win and other times it isn't; either that or I'm misreading the situation)
- the losing team has been in control of the point in the last ~10 seconds (might be more or operate on some sort of permanent timer i.e. 10 seconds of no point = no overtime and the timer does not reset at any point, so if you gain control after 9 seconds of overtime and lose it for a second later on, the game ends)
- the winning team does not have control of the point
lag may play a factor in some cases.
I'm still not completely sure how it works myself, but the above is the best I've been able to piece together