Here is the ruling. There is no time when passing between those two zones where you would not be in a zone with Fortified Position.
The difference between this and switching armor is that logically you can't have two pieces of the same equipment on at the same time. Like I can't wear two shirts.
On this, all creatures are in a zone. There is never a point where a creature isn't in a zone. So yes, it's simmilar, but it does not apply to this action, because you're always in one zone or the other.
As opposed to the previous ruling where you have to take off some equipment to put new ones on.