Mark, I think you underrate the influence of the sun. You are too much focused on your own situation in New England. And Maggi, sorry, but the Scotch are not familiar with the product 'sun'.
Let me explain a common situation in Western Europe, Holland, Belgium, Germany, Northern France, zone 7b, maritime climate. We are in the middle of June. After a Long period of cool weather, the wind is in from Africa, last night I couldn't sleep, Joni Mitchell sings. Temperatures raise suddenly to 30-33 degrees C. The sun shines from 4 am until 10 pm. The inclination is almost vertical. The purple coloured Acer palmatum dissectum burns within a few hours. The other herbaceous plants bow their heads, but will survive. Not the Epimediums. So a spot in the shade is an obligation.
I don't think I underrate the influence of the sun. But you are correct in that I'm focused on New England, of course because that's where I live and garden, so the notes I offer will have the most meaning for people in the same general area, or areas that might have some equivalency. We've had a very long and cool spring too, but I imagine that it'll be soon enough we'll get the full affront of HEAT, with our notorious heat-wave days that can last for weeks with temps reaching near 98-100 F (~37 C).
I did have the opportunity to garden in a drastically different climate, 3000 miles away in the Pacific Northwest, near Seattle Washington. I was struck by how different the climate was, 3 full USDA zones milder, yet plants were very much "softened" by the mild climate and abundant rain, then when a day that came along in summer that reached 84 F (29 C), an average day in New England, in this Seattle garden everything melted, drooped, and burned. A total eye-opener. So I do understand the difference.
My main point is, Epimediums realize their full potential in terms of best growth, best flowering and foliage coloration, with sufficient light. They will survive, prosper, and flower well enough, even in deep shade... amazing plants.