Currently my Vario is only being used for grinding coarse for french press in the office so I'm not tweaking any settings. When the hopper was 3/4 full I timed out how many seconds it took to get my desired dose. But today (now the hopper is getting low, not quite 1/4 full) something compelled me to weigh the dose and it was lower than I expected.

Does the amount of coffee in the hopper affect how fast a Vario feeds beans to the burrs? Or am I more likely looking at a grounds retention issue?

Hopper load mass will affect all timed dosing.

To expand upon Tom's reply: bean load makes a big difference. A heavier bean load results in faster grinding times and finer grind particles. A lighter bean load (particularly when single dosing) results in slower grinding times and coarser grind particles. This is not a subtle effect.