You should mix the CRF in with the top layer of media a little bit with a bamboo skewer of something. The CRF needs moisture to work. If it sits on the top it will dry out more quickly and stop releasing nutrients. But you don't have to mix it in completely to the medium. Topdressing the pot is fine. The waterfall effect will carry the nutrients down into the root zone.

I agree with the advice given above. It's usually best to add the CRF when you first mix the soil so that it gets blended throughout the soil, but you can still mix it in the top part of the soil with your fingers or a chopstick, etc.

I would not just sprinkle it on top of the soil and leave it however.

TYG

I like the idea of the waterfall effect too, but then again the tomato roots reach the bottom of the container very quickly, and it's nice to have a little CRF there also if possible.