Yield from staking

So let's say I buy blue jay coin for 50 cents a piece and paid $100 for 200 coins. Let's say the yield is 15%. Is that yield for the $100 or is that yields for the 200 coins. I know it seems like the same but coins go up in price and go down in price so they would not match in the end. What I mean is if it stays at 50 cents then I would either get $15 or 30 coins. But if the price fluctuates is the percentage based off of coins or cash value? Sorry I'm autistic and not good at explaining so you might have to pick apart what I say.