Answer: Unfortunately, I can't think of anythng that will fit your requirements. The Rose of Sharon requires full sun all day long or for a minimum of six hours including the hour of noon and is not winter hardy in your area. (Your zip code places you in winter hardiness zone 4.) The kerria also requires more than just a few hours of sun, a half day would be much better and a full day best. In too much shade it will be very long and leggy and will lean outward looking for sun -- and it will not bloom much. It is also typically over six feet tall and wide so it is way too big. It is also not reliably winter hardy in your area -- some varieties are only hardy to zone 5.
Depending on how much sun the area actually receives, you might consider Rhododendron x 'Ramapo' (H-1) which grows to about three feet and Rhododendron x 'Purple Gem' (H-1)which grows to a little over two feet tall. These both have purple flowers and and winter hardy into zone 4. They need organic, acidic soil that is evenly moist yet drained, and do best in morning sun or bright dappled light all day.
Your local professional nursery staff and county extension may have additional suggestions based on a more detailed understanding of your growing conditions where you want to plant and your overall design goals.
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