I turned my car upside down, and the draft gear box is definitely the first thing the wheels hit. However, if I position the trucks so that the wheels are just touching the tabs sticking out of the draft gear box, the intersection of the truck centrelines is 16” - 17” away. Removing the tabs brings it down to 11” - 12”.
Now I imagine with a bit of car rocking, axle drift, etc. you can’t quite get 100% of either of those. But I’d be reasonably confident the coal cars with the stock Accumates will go down to 21” curves, and with the tabs removed even 15”.
I do have some reefers, so I’ll do one of those next and see if it really is different (or if my test methodology just doesn’t match actual experience).