A pretzel conundrum

I made pretzels this afternoon, following the King Arthur recipe as usual. I always need two baking sheets to hold the entire batch, and the pretzels on the top sheet always cook faster than the ones on the bottom sheet.

Today, the pretzels on the top sheet were completely baked to a nice dark color in 14 minutes. After I took them out, I moved the bottom sheet to the top rack and baked them for three more minutes, but they were still not nearly as dark as the ones that had been on the top rack the whole time, as you can see in the photo below.

Baking friends, any suggestions on ways to get the two batches to cook more evenly? I guess I could bake the two batches serially – if I did that, would I have to wait to boil the second batch, too?