Have you considered a side by side, say dual 14-16U tall bays, in the upper area of that closet? (The lower area could stay closet space.)
You literally could take a used rack, cut it into 2 and flip one end, then frame it in up high. A removable back could give you rack backside,
from the closet. These racks are so flexible, and I have sectioned a few, and shrank my Slim5, with a $10 Harbor Freight 4" angle grinder.
I would recommend you take some av rack growth space, and blank off some bays.