Software development royalty rates

Hello, lovely people,

I'm not sure if this is the right place for this question, but I'll just give it a go.

I'm working as a software developer for a small company that sells a product used for medical/therapeutic purposes (don't wanna be too specific here, because of NDAs). We've been developing the product for many years now and finally it's on the market and sales numbers are looking very good. During development time I've always been promised royalties for every sold machine, once the company is earning real money. Now I just received the first proposal for that and well… the numbers feel a bit strange to me. I couldn't really find good resources for comparison on the internet, so I thought I'd ask on reddit if some of you might have experience with that.

For context: The product is in the price range between 10.000 and 15.000 Euro. Lots of my code defines the very identity of the product. They just offered me the following model:

I'd get 100€ for each of the first 40 sold machines. The next 40 machines would give 70€ each, the next 100 would be 50€ each, and from then on it's 20€ for every sale.

I don't know if it's just me, but it doesn't really feel fair to me. I'd be willing to talk to them about it, but it's a bit hard without having any idea about if there are any standards to compare with.

What do you people think/know?