Sometimes these maxims are true for a reason. My first attempt making a butter dish is a case in point. I measured a "standard cube" and figured for shrinkage, but didn't take into account that as a lid or half-sphere, the total inside dimensions would shrink, too. By the time they were high fired only a skinny cube with the end cut off could fit.
The maddening thing is that my volume-challenged husband immediately saw they were too small when he saw them. Argh!
Guess "back to the drawing board" should be one of my major subject categories for this blog.
Once I get one to work, probably in the $40-45 range.