Thanks again for all your input regarding my original question. I did finally email Sharp Corp. customer service and received a prompt reply, as follows:
After researching your question, the wire racks are not recommended to
be used while using the microwave portion of the unit. The wire racks
are only recommended when using the convection portion of the unit.
I emailed back to inquire about the "mixing" type use where the oven goes from microwave to convection, mixing the type of use, as someone above mentioned. I have not received a reply to that question yet.