How can I politely reject a guy without hurting his feelings?

I am going out with a guy , he is particularly lovely the conversation between us is very good. He appreciates me , gives me attention and time. He checks of all the emotional qualities a person would expect from the person they are dating or would like to date but still despite of this I don't feel physically attarcted towards him because he is shorter in height. Is it my shortcoming that I am so superficial that I can't see anything beyond his beight.

FYI - I am 5'8 and the guy in question is 5'6

How can I politely reject a guy without hurting his feelings?
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