@ replicand - many thanks for that information and demo!

Having seen my renders go blurry using Gaussian at > 1 pixel, I rather stupidly assumed it was due to the higher pixel setting, rather than the type of filter used.

Btw, if you get those (semi-)transparent lines at the bucket boundaries using the sinc filter, a simple fix is to copy the image to a background layer (in whatever postwork program you use) and offset it by one pixel vertically. Then merge the two layers.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)