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What's the source of the constraint on rocket size that you refer to?

The tyranny of the rocket equation means it starts to get crazy if you can't improve the payload fraction and want to send up more mass. I don't think there is a literal upper limit, but you very quickly get to the point where a few extra kilograms means you have to double the size of your rocket.

Isn't Starship planned to launch 100 tons into LEO, just with a two stage rocket, and with both stages being reusable? I don't know the numbers but this seems to suggest efficiency (cost per ton to orbit) improves with increasingly large rockets.

(Though I imagine there could be a size sweet spot beyond which efficiency shrinks again.)

And it needs to refuel to get to Mars despite being the largest rocket ever built and an incredible feet of engineering. The limits are height and space to put engines under it.

But that doesn't limit the rocket size in any way, only the fraction of its mass that can be used for payload. That limit does not depend on total mass of the rocket. Is there something that makes larger rockets less feasible than smaller rockets with the same payload mass fraction?

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