I don't know about mini petunias, but Calibrachoas do not need deadheading. Most commercial varieties of Calibrachoas are sterile and don't set seeds.

It seems to me that the problem with most petunias and calibrachoa is if you do nothing you end up with long tentacles' with a bloom on the end. I also think they are so highly hybridized that making a general statement is a mistake. Maybe if I didn't have so many I could keep track of difference in performance. I can't deadhead them I have too many. At this point in summer I start pruning back the longest tentacles to get the bloom back in the pot. Every couple of weeks I trim the longest runners off. I try to match pruning with growth. I respond to what the plant is doing. I pull the longest tentacle up in the air to judge. If it is a long row of spent blossoms, small leaves with a bloom on the end, the petunia gets a good hair cut. If it is a long row of spent blossoms with new branching too, I pinch the tip. It's like hair. If you never cut your hair it sticks to your head from the weight. By July some will stop blooming from heat or have gone to seed. The petunias left standing are the ones I will seek next year. My absolute favorite is from Proven Winners, Raspberry Blast. I babied them through the winter. I wouldn't have bothered if I had known Home Depot would sell them this year. I had a 20" pot of them in full sun last year, just 2 plants and they bloomed through our terrible dry heat. I did have to prune them at one point because they were covering everything in the surrounding flower bed. The center of the plant bloomed without pruning. It is sticky and a heavy stemmed petunia. I have many types this year and will see what is still blooming in July.
Calibrachoa are a mystery. I get a big mat that eventually stops blooming probably due to heat. I will prune them back then and hope for re-growth as temperature cools in fall. They seem to get shaded out by other plants in my pots and die. Or they move down the pot to get sun and in the end I have a bare stem with a tuft at the end. My best success is a patch under the grape. There isn't any sun competition and it is trouble free. I guess the answer is to use it as a ground cover! Mmmmm... I know just the spot.
To add to this rambling post, I have to spray with Bt for budworm. Raspberry Blast is the only petunia that I have had that will out bloom what the budworms eat. Snail bait is a must also.