Not necessarily – would you rather have a 10% chance to contaminate a 1-charge container, or a 1% chance to contaminate a 10-charge container? The expected value is the same.
Assuming normal rain (or normal acid rain), expected fill rate (in charges per hour) is:
[b](funnel_radius_mm / 100) ^ 2[/b]
The big funnel has a radius of 380 mm, so that’s (380 / 100)^2 = 3.8^2 = 14.44 charges per hour, on average. The makeshift funnel has a radius of 85 mm for (85 / 100)^2 = 0.72 charges per hour.
Drizzle and light acid rain produce half as much liquid as regular rain, so those expected fill rates are simply halved to 7.22 and 0.38 charges/hour when it’s drizzling.