Jeff,
Personal preference, I guess - - but I am now using two fertilizer strips along the front and back sides, about 3 inches in from the walls, and about 3 inches deep. I place one Cup of TomatoTone in each strip, then cover and slightly water in. Having said that, now without the cage getting in the way in the new design, I may experiment with the picture-frame application again, as this would seem to provide the best distribution of the fertilizer.
Again this Season, I will be trialing various fertilizers such as FloraMato to see which works best. I hope in about 5 years of trials, to get it down pat.
Glad to hear about your success with the Radishes. Post some photos when you can.
Raybo