Indeed it's very possible that it may likely have required some changes to the design/material to accommodate a larger overhang, but i'm also very sure this is something Metrolinx didnt even bother looking into unfortunately. Evidenced on how they plan on slapping virtually the same platform canopies on the Hurontario Line.I can't help but think that the problem then becomes a physics & materials problem then.
A larger overhang would require more materials, which may thus cause the shelter to be more massive and take up more space in the already-limited footprint of the platforms.
Consider the VIVA shelters, for instance. Yes, they are taller and cover some of the vehicle, but they are also considerably deeper on the platform to compensate. And yes, they've made that depth an enclosed shelter, but consider that they now also require a considerably wider platform.