Multitasking with oven ( roast and potatoes)
Here's what I'd suggest: 


Reverse your food positions. Roast the meat toward the bottom
of the oven and the potatoes toward the top.
Place the potatoes on a jelly-roll sheet, not in a
roasting pan.
Stagger the pan positions. The less that they are exactly on top of
one another the better. Yet, at the same time, no pan can be so
close to any oven wall that it cuts off circulation. So, choose pans
sizes that will allow for this. During baking, rotate each pan 180
degrees.
It takes more energy to heat more items. When you put more
items into the oven than called for by the recipe, you must increase
either the heat, or the time, or both.