Buy the apartment complex and install an XG91 on the roof. (Bad joke, sorry.
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A bit of metal railing can skew the antenna pattern quite a bit. Have you experimented with all of the reasonable variations of antenna location? Any windows with a southern view?
It's also entirely possible that you are getting a reflected or diffracted signal as the result of the building to the south. A little reverse engineering makes me think the complex at the corner of Clark Ave W & Yonge St could be a big reflector.
If you are using no more than 50' of coax, I doubt a preamp will help... If anything, it will add noise and make matters worse.
How about making friends with your upstairs neighbors. Would they like free OTA signal enough to host your antenna on their balcony?