Overview

The urns are relatively cheaply crafted (clay can be found almost anywhere) and they hold as much as a double chest while taking up only a single block of space, making them vastly superior to any other vanilla-based storage options.
I think it would be a good idea to bring them back down to a single chest in space until they can be vertically stacked or something.

Why would this feature be useful?

It would aid in balancing the mod's content a bit better.

There is an option in the config to scale down the inventory of the urns.

On a more serious note, the little urns and stuff should probably only have a single row of inventory space - this doesn't seem to be an option in the configuration currently.
The default of a double chest worth of slots leaves a bit of a poor impression on an otherwise very high quality mod, I really do hope some consideration can be made to reduce their slots!