Use this mod to hide the chestplate, the WaveyCapes will not cling to the back. Vanilla cape is normal

Curios/Baubles and other mods doing additional logic to the equipment rendering are currently not supported (there are plans for later). To be fair, in this case this is something the "Show Me Your Skin!" mod could fix by correctly removing the chestplate from the renderstate when its fully hiden, not render it at 0% transparency/skip the rendering at the last moment.