Volume of small taps, so fixed fees dominate
Thousands of small transactions is the same arithmetic as a café, only more so. Any fixed per-transaction component is the line that decides your card cost, well ahead of the percentage.
Least cost routing carries the same weight here for the same reason — almost all of it is small debit taps.
Nobody is standing next to it
An unattended terminal that stops settling does not get reported by a staff member; it gets discovered in a reconciliation days later, and every car that left in between is revenue you will not recover.
Monitoring, alerting and who is responsible for a fault are worth more attention than the rate. Ask specifically what happens, and how fast, when a device drops offline.
Reconciliation across multiple machines
Several terminals across several sites means settlement arriving in pieces. Whether each device reconciles separately or the whole estate reports together changes how long the admin takes every week.