[aussieshibe]

I've tried both. Standing is clearly easier.

There are three main parameters: stand/sit, front-to-back/back-to-front, front-access/reverse-access (i.e. between the legs or behind the back)

Back-to-front is a health risk for 50% of us, and just a bit gross for the rest. So rule that out.

Wiping hand between the legs is awkward and requires that the thumb (a notoriously larger-than-the-other-digits digit) is used as the primary wiping vane.

Sit + wiping hand behind the back + wipe front to back allows use of the index finger, but requires an awkward lean and lift of one cheek to gain access.

Stand + wiping hand behind the back + wipe front to back is, therefore, the only sensible option. Additionally it makes checking the bowlean return value indicated on the paper much easier.