Welcome to the New England forum. What a lovely yard you have!

I will start by saying that I don't grow this variety of Hydrangea paniculata, though I do have 3 other selections (White Diamond, Pinky Winky, and Quickfire.) I also have put some thought and planning into screening certain views in my garden, so hopefully I can contribute something useful.

IME new plants take a bit of time after initial planting to get to their ultimate shape. New plantings are putting much of their growth energy into establishing roots their first growing season. Your plants look like they are also blooming well, and IME H. paniculata varieties establish quicker than many other woody plants, so you will probably see additional vigorous top growth this coming season and thereafter. I'd wait until after the third season to decide whether they will provide the screening that you want. There is a PeeGee down the road from me that is out in the open on all sides like yours, and I will take a look at it next time I go by to see how close to the ground it wants to grow.

A couple of comments about your inspiration photo (IP) vs. your situation:

How sure are you that the IP is actually PeeGee? There are a bunch of different varieties of H. paniculata with somewhat different overall size; branch stiffness; blossom color, shape, and timing; and each has a slightly different look. Your photo is a bit too fuzzy to my eye to be sure which it is.

Your planting situation (open on all sides) is a bit different than the IP, which is backed by other plants. This has two potential effects on the H. paniculatas in the IP which could give them a different appearance than yours (but might not given a few years of growth.) First, this type of Hydrangea prefers a lot of light and the IP's backing of taller plants may be causing the hydrangeas to reach forward and weep a bit in its effort to get more light. Second, since there is more than one layer of plants, any gaps are covered up by the plants in the background.

So, what can you do?

You can be patient and see how they fill in once they really get growing. You may find that given a couple of years that they do what you want without any other planting since they naturally have an arching branch form.

H. paniculata responds well to hard pruning once established, and you could cut them back to below where they are currently sending out leafy branches to get them to branch out lower. This would leave you without screening for a bit when you did this, however, though they will grow back quickly (a couple of months).

Or you can do what I do when I want really dense screening; I plant 2-3 layers of plants so that any gaps are filled by other plants. So, you could plant some mid-sized perennials or lower shrubs to fill in the lower gaps of your PeeGees. To make specific suggestions that would be successful we'd need more information such as whether you are willing to plant on this side of the split rail fence and how much room there is on the other side of the PeeGees before the pool deck seating area, amount of sun, and compass direction of the view from the photographer to the pool. However, I've seen photos of Hydrangea arborescens Annabelle in front of H. paniculata, and there are a number of other possible plants that might work here to provide another layer to fill in gaps if they remain.

Here are a few blog posts from a Detroit area designer, Deborah Silver, that may give you some ideas. (Her favorite Hydrangea, Limelight, is another H. paniculata, so much of what she says about them would apply to your PeeGees.)

Designing with Hydrangeas

and here are photos of Annabelle with Limelight (fourth and fifth photos):

Hydrangeas

and some more photos of the same garden. You can see how having more than one kind of plant (in this case two kinds of Hydrangea) and more than one row can make for a dense planting, since I think this is just a year old. The H. paniculatas will get much taller while Annabelle will top out at 4'.

These two both have info on pruning H. paniculatas

Let's Talk Pruning

A Second Look at Limelight

Despite what she says about pruning H. paniculatas, I never prune my H. paniculatas. Here is my 6 year old Pinky Winky which has never seen pruners other than to remove the spent blossoms on the branch tips from the previous year each spring, and it is completely full all the way down to the ground. It's about 8' tall. I think that PeeGees tend to be a bit more fountain-shaped than either Limelight or Pinky Winky.

NHBabs, thank you so much for such a throrough and helpful response. I'm learning more and more it's all about patience. I like your idea about planting some additional varieties down the road if our Pee Gees don't f do their arching thing. Look forward to checking out the blog posts you provided. Thanks again!