Yes the interior design of a solar oven does affect its performance.
The one with the shiny inside and steel plate at the bottom got 10 degrees hotter than the second hottest oven. It also stayed 15 degrees hotter for 30 minutes than the second best oven, and 10 degrees hotter for 60 minutes. It stayed 35 degrees hotter than the worst interior.
A steel plate on the bottom of the solar oven on average increases cooking time by about1 hour.
A shiny interior reflects any remaining heat back to the food.
This could be applied in making solar ovens hotter, to use in places such as Canada which aren't as sunny as Ethiopia.