going from small package to large package

Hi~

I'm sorry if this has already been answered in a previous thread. I tried searching in the forums, if someone could point me in the right direction I would greatly appreciate it!

My question is about going from small packaging to large. I've set the max weight of my small/medium packages to 1.5 lbs, everything beyond that should fall under large. However at the moment, when the total order weight exceeds 1.5 lbs, it splits the order into two small packages instead of transitioning to the large package option. Is there a setting I'm over looking?

thanks in advance!