Hi milepig-

The reason for the handle side up when washing knives is your safety.

A wet, or semi-wet knife, when pulled off a mag bar, can slip down in your hand from the handle, with the sharp knife blade sliding down into your palm. Water or moisture being the best lubricant, it can compound the effect of a knife cut.

If the knife is not fully dry, or fully clean, it can happen. Bear in mind that the knife blade will dry downwards onto the handle, if the blade is stored on the rack pointing up. The blade may be dry, but not the handle, resulting in a possible cut, or laceration. With a very sharp and heavy knife, and perhaps in a rush in the kitchen, that could be severe, with a trip possibly to the emergency department for suturing.

Does this happen ? Yes, more often than you think.

A knife handle vertically up, or horizontal, is better as it reduces that risk: if it slips there is no problem, as the knife just falls down, blade first. A little sharpening and you are back in business. If you get cut, you're not.

Up to you of course, on how you hang your knives to dry.