My 1984 JC Penney microwave had a large square glass that laid in the entire bottom of the microwave. It split in two a week ago. I brought home a smaller round glass from a smaller microwave from work that sits in the center of the microwave and have been using it. It now does not take as long to microwave food and I'm wondering if I am doing the wrong thing by installing a smaller glass tray in the bottom instead of the much larger tray it came with originally. Of course, finding a replacement tray is probably impossible but can someone tell me if I'm doing harm to my food by using the small round tray. Thanks very much.