The Moon is on an elliptical orbit around the Earth and varies in distance by about 13,000 miles — hence when it’s further out, the Sun isn’t quite covered. Also, the closer to the Sun, the less the Moon will cover; the Earth is closest to the Sun in January, making the n hemisphere’s winters a bit warmer than those in the s hemisphere.
I knew it was elliptical, but didn’t know it was enough to do this. Thanks for the reply.