[dcb]

Like Pat said, a big factor is the side area/weight ratio.

cylinder equations:
volume = r*r*pi*h
side area = r*2*h

examples

height 1, radius 1
Volume = 3.14
side area = 2

height 1, radius 2
Volume = 12.56
side area = 4


so doubling the radius, doubled the side area, but quadrupled the volume (i.e. amount of sugar water). Of course it matters how much the feeders were filled, and if there were any wind shielding variables.