(re-upped the blueprint--I hadn't set demand properly.  Fixed, though when you paste it, Blueprint Tweaks reports the ore demand is remote-demand and local-supply, despite it building as demand for both.  Dunno what's up with that, but it does print properly.)

First off, go look at Ludus Machinae's belt-bending artistry, in particular their  "Vertical Belts" blueprint!  That blueprint lit a fire, and after an attempt at reverse-engineering it, I made the original Short Stack.

After a nice conversation with Ludus where we swapped notes (as it turns out, we arrived at vertical belts using two completely different methods!) V2 is a refinement using those swapped notes, namely in that it uses full-step vertical belts instead of half-step ones.  This cuts the total belts needed by about a third.  The functionality is the same, namely that this is a really compact 180-smelter array.  Each row is only 4 units tall in latitude, and thanks to the vertical belts, there's no extra space needed in which to put Tesla Towers--they fit right between the in/out sorters.  That lets me "fold" the typical 30-smelter line in half so six rows will fit into 24 units, which are then duplicated on the other side of the ILS.

Handy features include:

All the ore output slots are easily accessible on the "open" sides of the ILS.  If you don't use Blueprint Tweaks, this is still an easy blueprint to swap over to a different smelting product!  No reaching into a rat's nest of output belts to change up the slots, just six nice and easy-to-reach ones.

Output is on the topmost belt so that you can easily see the array's status.

Each row's input belt peeks out from under the output belt at the end so that you can also see status of incoming ore.

These will slide right against each other with no ILS placement troubles.  You can fit two into the first tropics right next to each other.

Likewise, no issues with overlapping Tesla Towers on the outside row--they're tucked deep into the array to avoid "too close to a power station" errors.

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If this design has a flaw, it's that it doesn't saturate immediately like other smelters.  The extra belt space used to make the vertical rails means there's a pretty fair amount of buffer to fill before all the smelters get a proper feed.  That said, if used in a high-demand, high-supply situation, it'll saturate just fine after a while and behave like any other smelting block...just smaller.