There do exist many a cost that do not change, regardless of yard size.
The time it takes from when the truck pulls up until the lawn mower is on the turf.
The time it takes to put the mower back on the trailer.
The time it takes, to pull and start the trimmer, then to shut it back down and put it back.
One more time for the blower.
And to load everything back up.
None of those times above change, no matter what, it takes just as long.
I have done yards so small I literally spent more time just swapping around than doing actual work.
Still it took dang nearly 20 minutes, no matter what.
And yeah, then there's scheduling / deposit / maintenance / etc.
These costs, for the most part, is what my minimum consists of.
It's not to be a wise guy, it's to cover that.