My dear friend has this exact set-up. When I landscaped around it to camouflage it, I cut a bed around all the caps.I did smallish evergreens (topiary, spiral arbs & standards) on the ends & grasses & perennials between the caps in the middle. The point was to have some "hindsight", if it ever had to be dug up, the perennials & grasses are easily removed or replaced. Then on top of the caps, I put a wishing well & a couple wooden chairs with the seats planted. it totally takes your eye away from an eyesore. For the most part you don't even know what's there. hope this helps.
I just went back & looked at your pic. yours looks to be situated pretty close to the patio.What you could do is incorporate it with the existing bed on the right & throw a bench in there to have another small seating area. That's a nice setting, BTW.

Dee67: Thank you. I think it would be nice to extend the garden bed towards it, and include a path.

You got it! I see a complete wildlife walk through garden in your future.