A progressive is typically set at 1/8th of a cent. .0125% .00125
The amount contributed is typically inconsequential to the house hold, and is written off as a marketing fee vs income at the Casino.
The base amount of the top award usually starts at the top award of the machine.
If they did not use at least this amount and someone won on the first spin, then that would theoretically alter the %% payback from the stated norms which would be a violation of the gaming regs.
You will see a lesser amount in less regulated places such as the Caribbean, and when the progressive starts to add up they tend to dial it down and pocket it for the casino.
Sometimes the casino will jack up the amount of the progressive, usually this is in cahoots with the slot manufacturer as a promotion of some new hot game and is underwritten by an insurance company.
On my personal home progressive I set mine at 4% .04
This way for every quarter inserted the progressive goes up by 1c
More or Less I don't trust my own wiring and this gives a immediate visual that it is working.
You would never see that in a casino.
Just as another data point - From a hold percentage slots usually pay back between 95.5 and 98.5 meaning the house hold is 4.5-1.5%.
You would never see them putting their entire margin on the line.
They say slots have no overhead - Ie they work 24/7 without sick days, but they do take space (rent), do take energy, and do require some maintenance even if that is simply emptying the bill hopper and filling the thermal printer. The casino needs to make some money.