Stat wise it is marginally bigger than the titan and could definitely fit in a warehouse. I was less talking about the lore and more about why not use the larger stat block. I mean 20' wide by may 25-30' is not much bigger than 15' wide and 18-22' tall.
So, I have some time and I’m less annoyed that my DMing decisions are being put under the microscope for no discernible reason, so I’ll reply to this part.
To me, a construct the size of a big SUV is about right for what I was doing. Here’s a thing made to go to war, to be relatively easily deployed, that has been modified in design to serve the purpose of urban terror. It’s about as big as you can go and still be able to put a few of them on an airship, or one on a large skycoach, or be hidden in a convenient place, etc.
As for the platforms, you’re talking about a roughly 15ft+ wide at least half that from top to bottom, disclike torso. It’s easy for me to imagine raised shields with archer window style slots, that can fit an average human with a crossbow or war-stave. Basically, thier lower half is inside the body of the Titan, thier up half is mostly shielded by a raised “wall” like you see on emplaced gun positions in movies.
And a nearly 20ft tall, 15ish ft wide, construct with weapons on the ends of its arms the size of an average human, is pretty terrifying.
Tactically, on a grid, I didn’t need it to be gargantuan to do the job. Huge takes up plenty of space, and is big enough for PCs to crawl around on it without it basically being terrain. I’m saving that dynamic for a later fight.