Warm air rises and cold air sinks. If the air is not disturbed/circulated much, the cooler air in the room is toward the bottom. So more frost is likely to form at the bottom of the windows.
You can help us out by revising, improving and updating this answer.Update this answer
After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.