When you direct the spray upwards, it not only covers the under side of the leaves, but some of the spray also falls on the top of the leaves as you make your way up to the top of the rose bush. Once your at the top of the bush, a spray over the canopy of the plant usually covers the whole plant quite well.

Blackspot pressure is only average in my garden and I get essentially complete control when I spray about 50 bushes biweekly with a gallon of BannerMaxx. My technique is to make two quick passes over a bed, spraying each bush twice. You might tailor your spraying to suit your conditions and fuss about hitting each leaf or covering the bottom side of the leaves only if experience shows that it's necessary. It is true that the usual rose systemics will not translocate from a sprayed leaf into an unsprayed leaf to any useful extent.

I agree that minis present special problems. I have a few susceptible minis with very dense foliage which hugs the ground and creates ideal conditions for disease. I suspect what I really should do is replace them with more resistant varieties.

The secret is to have lots of pressure behind the spray. The more pressure, the finer the mist resulting in the best coverage. Powered sprayers tend to have greater pressure, thus a finer mist.
Mine has a four foot wand with a nozzle that breaks the droplets into very fine particles.
I poke the wand facing up under the bottom of a bush, The force of the spray forms a mist that coats all the under portions of the leaves and allows the overspray to settle on much of the leaf top surface. A quick overspray of the canopy covers the rest of the upper surface. Mine was built by Ken Muncy.
Another one is the electric Atomist sprayer. It does a great job in very little time. The blower creates a fine mist powered by a stream of air that blows away any loose leaves and covers all the leaves with a quick pass. The spray will do a tall climber or get hard to reach bushes. The drawback is the electric cord and small tank. On the plus side, you get done in half the time using half as much product.
They can cost over $200, but I've seen then a little cheaper by searching on google for the atomist 1026B
The one gallon pump up sprayers have to be pumped often to maintain enough pressure. As the pressure decreases the droplets get larger, covering less area and using more product.
The one for garden applications is on the left.
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Does your sprayer have a wand? You should be able to reach the ground without bending and/or tip the wand up to reach the undersides of the leaves.

And as Karl says, the finer the spray, the easier it is to cover more area.

Lots of good advice above. Have you also determined which bushes need spraying? I usually spray only the ones that have BS problems. My Mayflower, for instance, never has had the problem, so it doesn't get sprayed. Of course, the only way you can find out whether a rose needs it or not is to let it go unsprayed to see how resistant it is. Even though any rose that makes it into my garden better show some disease resistance, some roses are much more resistant than others are.

Once in a while--during peak BS season, for instance--I may spray just about every rose once or twice, but my usual spraying includes only about half of my roses.

On the other hand, I'm a lazy sprayer, so you may not want to follow my practice. LOL

Kate

Since I didn't spray early in the season, I started to have a BS problem, especially on Heirloom HT, but also others. So I started to spray everything in my small collection. At my last house, I knew nothing about BS and I can say that all the bushes were dropping lower leaves by late Summer.

I believe in my climate that most growers who spray do spray everything but I will check with locals. I was spraying the tops and bottoms of the leaves which does not sound like standard protocol based on the recommendations. Maybe I will do as suggested and spray the undersides and a canopy above.