How tall are you wanting and to flower when? Rudbekia Herbstonne, Anemone japonica [jap anemone] are both 4-6ft tall and flower now.

there are Leucanthamums [shasta daisies] for early/mid summer, Echinops, Phlox panniculata may be ok too.

Some of the Asters would be happy there too. We have one flowering now which is well over 4 foot tall. No idea of the name though.

I have a similar situation and have Rudbeckia and Verbena bonariensis. I have grown a shrub Indigofera kirilowii the Indigo shrub spread out and pinned to the fence makes a wonderful backdrop. I know SBG loves her Japanese anenones but in my garden they are so invasive and I'm struggling to get rid of them

I’ve got a phlox there but is not happy in dry spot, wilted most of time. About 6ft or taller, was thinking with grey foliage with being drought tolerant?

How about Eryngium (Sea Holly)? Once established it's happy in dry soil of any kind and the bees love the blue flowers.

Got some of that already in border, but thanks for suggestion. What do people think about rose campion? It does tend to flop though. Need something quite rigid at back of border that holds its own.

Maybe Adam's Needle (Yucca filamentosa), some of the taller varieties of Gaura lindheimeri (best against a dark background), Helianthus maximillianus, and/or Butterfly Weed (Asclepias tuberosa)?

Eucalyptus?

Rose campion here doesn't get tall enough for what you want. Eryngium is OK in dry ground.How about a root or two of Florence Fennel? Makes a lovely dainty wavy background and will grow around 5 feet tall..

Stergram - I’ve got bronze fennel but never heard of Florence fennel?

It's the kind that makes the fennel bulbs that you see in the grocery store, Amsterdam.