I planted purple coneflowers and shasta daisies 'Becky' very late last August in a bed that I thought, at the time, was full sun. Well, it was full sun in the spring, but come summer when the maples leafed out, I found out that it didn't get sun till about mid-day. This has caused many of the plants to lean toward the edge of the bed. The coneflowers and daisies are the worst offenders with legginess, so I am thinking of moving them to a sunnier spot. Also, three of the four Eryngium varifolium I planted have died over the past two months.

My question is what sorts of summer-blooming perennials might I replace them with?

The perennials that seem to be doing well in that same bed include:
Sedum 'Autumn Joy'
German Statice (kind of leaning, but it's not too tall, so it doesn't look terrible)
Heliopsis helianthoides
Gaillardia 'Arizona Sun'
Gaillardia 'Burgundy'
Rudbeckia
Hemerocallis 'Siloam Sugar Time'
Budleia 'Purple Haze'
Agastache 'Lilac sprite'
Russian sage 'Lacey Blue'
Winter savory, tarragon, sage, oregano, chives, and other herbs
Everbearing strawberries
Rose mallow 'Disco Bell Mix' (not yet blooming, but doesn't seem to be leaning into the sun)

I won't lengthen this post to include the spring blooming perennials and shrubs. I just wanted some ideas about summer-blooming perennials that won't get too leggy in morning shade/afternoon sun, mainly to replace the stands of echinacea and shasta daisies. I don't have a color scheme (if that isn't obvious), and I have already considered having to revamp the bed significantly if needed. I am in zone 5a and my soil is ever so slightly alkaline and a bit clayey, though I do amend with peat moss.

Thanks for any suggestions.

Also, I would suggest long-term you may have issues with the Russian Sage, the butterfly bush, and the hibiscus, as all three of those just won't bloom without adequate sunlight. But, hard to say, as each site is so unique, just watch what the do this year and you will probably get a good idea of long-term potential.

Overall, I am just so confused with the parts of my garden that aren't obviously shady all day. I'm growing shade and part-shade plants in sites that remain dappled through the summer, but I'm finding the sunnier sites much more difficult to plan for.

I have been eyeing a part of the lawn that I thought was sunnier, but it seems to be sunny only till early afternoon. I thought that part-shade plants wouldn't do well there, but am rethinking my planting strategy based on the mixed results of the bed I describe above.

Right now the sunniest site seems to lie on the north side of my house--something I didn't expect, though if I think about it, my 'north garden" gets what to my neighbor is southern light.

If 'mid-day' means noon and then you have sun till...5 or 6 or beyond, well than that is full sun in my books. To be honest I have plants be successful in 4 hours of good sun that are described as being "full sun".

(Btw, I went out right now and snapped a picture of one of my stands of Beckys. They can be quite large. This one is as we speak 4 feet tall and over 3 feet wide. It is near the end of its bloom period after doing well for about a month.)

I'm really itching to fix the bed because while the blooms are cheerful, the growth habits are really driving me nuts! I see your point, however, about being patient and seeing the border through another growing season. (Give me strength!)

Thanks so much for your input.

Last year I planted a 30 foot long bed. The far end of it is next to a mature Japanese maple. To my surprise, the end was not in constant shade and actually got afternoon sun for a good two - three hours per day. It definitely impacted my plant choices.