Distortion with mfwdtran map projection

I'm plotting the footprints of buildings taken from the Open Street Maps data set. I've converted the lat and lon coordinates to Cartesian coordinates using mfwdtran. The buildings I'm plotting are in New York City so the UTM zone is set to 18T.

The building footprint is more distorted than I would like it to be. I assume the distortion is due to the large size of the UTM zone definition. Is there a way to refine the location of the map projection to reduce distortion?

Here is an example of the distorted building footprint. Note that the corners are not right angles:

[archlab]

Turns out the axes aren't equal. Whoops!