Instead of using mint leaves as a whole/chopped in the raita, I first make it into a paste and then add which I think imparts a more substantial minty flavor to the raita. Take a few leaves of mint and place it in a processor.
Grind it into a smooth paste/sauce. You can add water or yogurt to do this if needed.
Meanwhile take the yogurt in a bowl.
Add the mint paste/sauce (add little at first) , roasted cumin powder, little salt to the yogurt.
Beat well until smooth. Do a taste test. If you like a more strong flavor of the mint, add more of the mint/sauce. Better top add little by little cos otherwise it might turn out to be too strong for your taste (of course you can always adjust with more yogurt if that happens)
You can optionally add regular onions or spring onions if you want. I add them to make the raita more substantial yet making sure that the mint taste is not lost.