i personally think that there should be some sort of percentage of the overall time for a disconnect as opposed to a set limit under any time limit.
i think it's like 2 minutes or something now, but i think it'd be better if it was something like 25% of the total time of the game sort of thing.
I have just lost a winning position in a 30 min game because my connection failed for 5 mins. Surely, in a longer game, the time allowed for a disconnect can be less harsh.