I noticed that the Upgrade Finder is listing Off-hand items as Main Hand. Looks like the Off-hand items are also being treated as Main Hand when calculating value.
This is just a display issue, we’ll fix it in the next update. The ranking is working correctly.
For more detail: to properly rank an off-hand item for e.g. a Mage, we need to pair it with an appropriate main-hand weapon. Otherwise the ranking would never say to get an off-hand if you e.g. currently have a two-handed weapon equipped: of course taking off your weapon and putting on an off-hand with no weapon is a terrible idea!
So behind the scenes we create a combination weapon+off-hand to rank off-hand items. That combination is equipped in the “main hand” in the optimizer, so it’s reporting that on the result. For these items it should show “off hand” because that was the item in question though.
(Our optimizer does what Blizzard should have done about 10 years ago: it does not have the concept of an off-hand weapon slot for casters. There is just a single weapon slot. We create “virtual” items that are the combination of a one-handed weapon and an off-hand, and rank it exactly as if it were a two-hander. They are functionally identical, with identical budgets.)