I have read and seen how metallic reflective surfaces are used to block and reflect heat radiation from getting to more sensitive parts. this would make sense to install for example aluminium shield there, between heating element and the oak, so that it would prevent most heat radiation from directly reaching the oak. Of course the shield will get warm too, but nowhere near the temps of heating element and thus will radiate many times less energy towards the oak. And if this aluminum shield would be installed so that there is little airgap also between the heat shield and oak, the temperature transfer from conduction would be much less and I think these changes will lower the temperature of the wood considerably.
this is more or less what i do and it works a treat. except i use 0.010" thick polished stainless steel sheet (highly reflective).
There is a 1/2" gap between the heater coil and the stainless shield, and a 1/8" gap between the shield and the outer wood cube.
my oven tube extends through a hole in the top of the cube, so i use a punched stainless steel disc to center the hot glass in the opening so it doesn't touch the wood on the top - keeps the wood much cooler.
dead air is a great insulator.