Have you done many miles with those panniers so close to the silencer outlet?
I would carry ice cream and champagne in the LH pannier, hot dogs in the RH pannier.
I took a run into town and back this afternoon, about an hour total, got back, left it idling and made a video of me putting my hands fully on the muffler body, very slightly warm, moving my hand to the end, still negligible warmth. No heat shield needed, at all. Only the angled metal outlet pipe was warm and I could still grab it barehanded no problem.
The panniers could be contacting the silencer body with no damage, and that's with no airflow moving over it.
I tried uploading the video but a message told me the file was too large for the server. I can send it to anyone interested or worried about heat from these mufflers, no issue whatsoever.