The answer, essentially, is 'however big they need to be for the scene'. It appears that DFB scales the models to make them best fit what's going on, making their sizes inconsistent between episodes.
Compare Plunk on Titan Camera's hand in episode 51:
Versus Plunk in Titan Speaker's fist in episode 57:
Plunk appears considerably bigger, even taking into account that TSpeaker is a bit shorter than TCam!
Here's an attempt at scaling the screenshots so Plunk's head is the same size and lined up. It's tricky, because the heads aren't at the same angle, Plunk is very small on-screen in episode 51, and Plunk has a black head against a mostly black background. But it'll do, I reckon.
Notice how much tinier TSpeaker's hand appears!
We can get a direct size comparison of their hands in episode 57. TSpeaker's hands are a bit smaller than TCam's, but not by that much:
And a nicer one from episode 64:
Let's re-add the silhouettes of the superimposed hands from above. Bit weird looking, because we're comparing TCam's palm-up hand to their palm-down hand, but we're just after a size comparison.
A crude attempt to scale down TSpeaker to match the hands we're working with:
Ehehehe! Smol!
Conclusion: the fandom wiki writers are absolutely wasting their time saying this or that Titan is exactly 72m tall or whatever. Skibidi Toilet is at its core a shitpost, so the Titans are the size they need to be for it to be funny when stuff happens.
