I think it's quite a common convention in engineering - not just software - that the input to a process "goes in the top and out the bottom". We humans read top->bottom (regardless of left/right/vertical, I don't know any languages that write bottom up). Conventional voltage in circuit diagrams usually flow top to bottom. Gravity loads in schematics flow top to bottom. Chemical pathways are usually written top to bottom. And of course functions take arguments up top and return at the bottom, maybe with some short circuits. I think the only counter example of note is distillation columns.

Where is the data coming from? Employees table. What's coming out? 20 rows of sum_gross_cost.

What could improve this is function signatures. It's kind of nice to have the whole abstraction up top...like an abstract.