Do meteor showers start slowly each night? Does the frequency of the number of visible meteors during a daily shower start off lower at the beginning only to increase as the night goes on or does the frequency remain the same for the entire night?
The number you are able to detect increases as it gets darker.

The number occurring is apt to be greater when the zenith of the sky is closest to pointing in the direction the earth takes orbiting the sun 
(like a windshield hitting more bugs than back window when a car is moving forward)  

The last factor I can think of at the moment is the density of comet tail material earth happens to be passing through (in its orbit around the sun) 
Which could unfortunately be not when your local the zenith is 'forward in our orbit' and when it is dark.