In practice tipping is mostly a question of tippers subsidizing non tippers. It’s just another form of price discrimination designed to extract maximum value for a business as employees would change jobs if they didn’t receive sufficient tips just as they would when underpaid doing anything else.

The difference in effort delivering 2 vs 10 items isn’t anything close to linear with their cost. I would suggest a fixed minimum + low percentage of the total order is vastly more reasonable than assuming you need to tip some silly multiple of the total bill. But even butter is to simply avoiding all businesses that use tipping, it’s both less mental effort and generally cheaper.