The low-res panel can be zoomed to the largest suitable multiple of 416. The high-res panel, on the other hand, needs a multiple of 832.
For, say, 1920x1080, this doesn't matter - 1664px wide is the highest multiple of both of these that fits. But there are some sizes where the low-res panel can indeed zoom to a higher size than the low-res panel, most notably 1366x768 - the low-res panel can zoom to 1248px wide, while the next step up from 832px for the high-res panel, is too wide to fit.
I really need to keep this explanation on copy-paste...