Yes, it's a flat fee, it only increases if you want extra coverages (full pay on day 1 of sick leave, unenmployment, etc).
The mandatory minimum doesn't increase which income†, but since you are also paying towards your retirement, you can choose to pay more, if for example you are in your final working years, so that you get a better retirement. But I'm not thinking about that right now :)
I am not the right person to ask about these things, and I may be wrong, but I think the workaround you are suggesting would cost, in the best case, the same as being autónomo on your own. You'd be paying about 250 € in taxes for a worker with the minimum wage (758 € in 12 wages).
†: of course you will have to pay income tax later (annually if >=70% of your income is B2B, quarterly if not, so many random rules!).
The mandatory minimum doesn't increase which income†, but since you are also paying towards your retirement, you can choose to pay more, if for example you are in your final working years, so that you get a better retirement. But I'm not thinking about that right now :)
I am not the right person to ask about these things, and I may be wrong, but I think the workaround you are suggesting would cost, in the best case, the same as being autónomo on your own. You'd be paying about 250 € in taxes for a worker with the minimum wage (758 € in 12 wages).
†: of course you will have to pay income tax later (annually if >=70% of your income is B2B, quarterly if not, so many random rules!).