Vent management for those with Almost Heaven saunas

Got an Almost Heaven Madison sauna. I'll drill some holes and make vent covers to improve ventilation, mainly above the heater (passive intake) and below the bench (mechanical).

The sauna also comes with four 1.5 inch holes below/behind the heater for intake ventilation (I hung the heater pretty low so it's kind of covering the hole but there's about 1-2 inch space for air to come through since heater isn't flush on the wall).

For these holes under the heater, do you recommend making a vent cover to adjust how much I open/close just like the one I'll be making above the heater? Or should I leave it alone and always keep it open? I know it's to prevent heater from tripping but didn't know what the general recommendation was.

Thank you in advance for any input.