I could be wrong, but I heard when coke is cut, some of the cutting agents will make your nose run. I've never had a runny nose with better coke. One of the best cutters is Inositol(sp.). I know somebody that cuts it with that and I tried it to see if I would get runs and I didn't.
There could be other factors such as volume - with ketamine you do a tiny line, and one line will do ya for the evening.. with cocaine you rail pile after pile, all night long you just snort and snort .. I'm sure there is some better explaination I am missing..