Earlier quoted context omitted.
I suspect that when I tip online for pizza it automatically gets bumped to the lowest priority of all of the driver's deliveries. He already has my money, and prioritizing all of the cash-tip orders over mine gives more potential for earning tips. Of course, my sample size is too small to say anything conclusive. After it felt like I was noticing a pattern a couple of times I just switched back to tipping cash.
When I've tipped online for pizza, and tip pretty well, I tend to get my pizza very quickly with a driver wanting to please me (like one time an order was messed up slightly and he immediately drove back and brought a new one without me even asking). My vague guess is that if you leave an above-average tip on an online order, the order gets immediately grabbed my a delivery person since they know they'll get at least…
Next time I order delivery I'll have to try a giant tip and see what happens.