Answer: Your zip code places you in zone 6B, the warmer part of zone 6, so your observation about winter hardiness would seem to be reasonable. Keep in mind that microclimate can have a significant effect on the actual hardiness zone in your yard -- depending on that, you might be a true 6 or you could be as warm as 7A. In your case, it is apparently more to the 6 end of that range.
Unfortunately the witch hazels are too large, as you said, and they would do better with more sun in terms of flowering anyway.
You might consider the deciduous natives Enkianthus campanulatus and Fothergilla major "Mt Airy" -- both are delicate looking and lovely in bloom, plus offer fall color. Or, possibly Pieris japonica (an evergreen, can be trained in small tree form over time with age although smaller cultivars are also available.) Your local professionally trained nursery staff may also have suggestions based on a more detailed understanding of the growing conditions where you are planting this and your overall design goals. Enjoy your new shrub!
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