Find ceramic tiles (any will do) and build a ceiling on the shelf directly above the area where the convection fan is. The goal is to build a ceiling that completely (relatively air tight) isolates the bottom of the oven from the top where the thermostat resides- use foil to fill any gaps left by the tiles. By blocking the thermostat, you can drive up the temp in the bottom area quite a bit further than 500F. Make sure you use this with the IR thermometer you're getting, and don't leave it unattended. Try placing your bottom stone on different shelves to see which gives you the fastest browning using the convection feature.
Also, check the ingredients of your flour for either 'malted barley' or 'enzymes.' If it contains neither, you need to drop your IDY (perhaps to .4%) and extend your fermentation longer- 2 to 3 days.