IX--point of diminishing return?

Am getting ready to make an IX UQ. BWDD's plan calls for 3 layers of IX and the info mentions that should have a range of ~35-40 degrees. So, I was thinking of adding an extra layer of IX to the UQ I'm making. This made me curious whether adding the extra layer will get me down to lower temps, or is there a point of diminishing returns that adding additional layers would just be a "recreational DIY" exercise. Looking for advice from those of you that have made IX UQ's. Thanks!

Tagged for curiosity, although I think I know the answer... I will hold my tongue...