I'm familiar with the bundled wire tables and single wire ampacity in free air, also ambient temperature adjustment going up to 1.04 for cooler ambient. I've found a couple references to direct burial that are for higher voltages.
Can you point me at a link that addresses our sort of application?
Not that I can't imagine cool thermally conductive earth helping with heat dissipation, but I'm not sufficiently versed in NEC.
Thanks.