How does POS interest really calculates?

Hi, hope this post is under the right section..

I need some clarification as I have had mixed messages from actual coin developers regarding hos POS is actually calculated and divided out to the network.

1) Say I have a coin that guarantees 10%pa interest (pure POS).

2) I have 1 million coins in a wallet

3) I should be generating 100K newly minted coins pa (or a bit more if compound) or roughly 270 coins per day.

I need to know if say for example 30 people on the network had 1 million coins would we all generate 270 coins per day guaranteed. (dev #1 told me this would happen)

or

would all 30 people be competing to stake thus making it more difficult to reach 10% pa or 270 coins per day? (dev #2 told me this would happen)

I need to know 2 things:

a) If POS interest is about competing or depending on who else is generating stake will effect your mint %
b) Is their any way of tweaking the code to ensure 10% is generated no matter what the case is and no matter who has network stake generating etc..

Basically the ultimate goal is to ensure everyone on the network can guarantee 10% or any fixed percent thats built into the code.