Half-day sun is adequate. If they are blooming so little, there may be something wrong with the soil drainage or chemistry, or they need more water and fertilizer. Pruning by 1/3 would probably encourage more bushiness. However, if they are leafing out, pruning now would postpone the spring flush of bloom by a month or so. Normal pruning is done around the time the plants start into growth, or in this case you can prune after the first flush of bloom.

I would say, you aren't pruning a tree rose, you are pruning a floribunda, and of course they can take severe pruning. Deadhead so that when all the stems are deadheaded, you have a relatively compact shape. Eventually it will fill in. It may be possible to train some stems over into the gap if you want to hurry that along.

If it were a climber, I think it would be very obvious by now. I thought I bought an Iceberg, but it turned out to be a climber by the Fall having planted it bare root in January. It was VERY clear that it was a climber, and it still is.

@irisgal: No. Not talking about the bare leg look. My bushes are just not flourishing with lot's of roses like I see in photos and local garden places. @cecily: Thank you for the welcome. I was nervous to post anything. When I deadhead, I prune where the next three healthy leaves are located and cut on an angle. @diane: I use Bayer All-In-One Rose & Flower Care and Rose-tone. Plus I give them banana peels and coffee grinds. My neighbor has many of the roses I have because we are a couple of garden geeks together. Hers thrive. They get more sun than mine, however I feel that 6-7 hours should be sufficient. I need to test my soil this year. How do you test your soil? Buy something from Home Depot or Lowe's or send out to a University?