Not many photos of Encyclia mariae growing in nature. Here's one where you can just barely make out the pseudubulb...which does not look like it is growing upside down...
Euchile mariae on Flickr - Photo Sharing!
Mine is grown outdoors, mounted upside down and is just starting to spike. When I mount an orchid upside down it's for stability. The only exception of course being Encyclia citrina... which likes to grow that way.
I don't think I've heard of anybody growing Encyclia mariae in pots...mostly mounted. Growing it mounted has the advantage that if you accidentally "over-water" during its cool drier rest it will dry out faster if it's mounted than if it is in a pot. I heard of one grower putting pots of Lycaste on their side during their rest in order to distinguish them from the more regular water requiring orchids. I think most growers just establish a separate section in their grow area for cool drier rest orchids.
Temperature wise...my Encyclia mariae had no problem with this last winter's low of 33F. Here's the average temperature range that Encyclia mariae experiences at one location in its distribution range...