Surface area, yes, but the inventory slot count remains the same.
I realize as I type this, it would be impossible to have one localized spot where a Linked Chest has an increased slot count due to being merged, but the same chest link somewhere else as a singleton...both would...yet shouldn't have an increased slot count.
Nevermind, thanks for rubber-ducking this one. Linked chests are OP enough anyway withiut giving them hundreds of extra inventory slots.