Hello Zone 6
I too have tried growing roses in less 6 hours of sunlight a day. For me, it is a matter of getting them out of the wind and cold. I have some success, they do grow, they might bloom, and often the colours hold well, but it is all pretty weak growth, and the blooms are not what they should be in size and fragrance and abundance.
I am slowly learning that I don't have time to run a plant hospital. If I can't give my plants the best situation ( soil, water, sun, temperature) then it is time to re-think the plant.
I love my Austins too, but some thing are not meant to be. 3 hours of sunlight is not a lot of sun.
Chris