You might go measure some of that white text on roads.

hhp

I think scale models would be helpful, even one as simple as a drawing on a sheet of paper that you view from an angle.

Or maybe you could use a projector to give you an idea of the proportions you need: Project the image of [non-distorted] letters onto the wall at varying angles, look/walk up and down down the hallway, and find out when it looks right.

Here's one potentially interesting precedent: L2M2: Kreissparkasse Ludwigsburg
I like how they employ the rather dramatic effect of the distorted letters, combined with a secondary system that is legible from up close.

If you go too crazy with the perspective/distortion (like here) you win awards but I'd be worried about confusing people too much (at least if the stuff *needs* to be legible).

I made a few scale models and found that very little expansion was actually helpful. It's only a couple of letters, so if you can see them at all, you can make out what they are.

I'd seen the garage in one of those design award books before, but I'd never looked at the pictures that closely. It's painful. And the office is worse! (In a good way)

I'm not trying to mess with perspective; I just want it to be legible from afar.

I'll look at the letters on roads.

But considering that expansion didn't seem to matter much, I'll probably decide such that the letters fill the space.

The height of the wall defines the maximum type size. The letters all have round counters, so that combined with the style of type leads to the width of a roman weight. Then I can expand the letters and make them bolder in order to fill the wall.

The space I have is such that this should give expand the letters by no more than one width.