I read from Ms. Tewksbury that a kilt that is even 0.5" too narrow is noticeable, as the underapron shows.
For this reason, she said she makes her kilts 0.5" larger in the waist and hips than the client's actual measurements, to give some room for growth, and then she sews the straps at their correct location.

The instructions in The Art of Kiltmaking say that following the book, the resultant kilt will fit the wearer with the straps in the tightest position. Typical kilt straps allow somewhere around 2.5" of adjustment. Unless I'm mistaken, that means even if the kilt is made 0.5" wider, in the loosest strap position the kilt will still be undersized and show 2" of underapron. Maybe strap adjustment is already accounted for, and this won't happen? But if that's the case, why add 0.5" to the measurements in the first place?

On the other hand, Ms. Tewksbury posted a picture of a woman wearing a kilt where the buckle strap locations had been tightened 10.5", and it still looked great (Special thank you to Ms. Tewksbury and her model for sharing those pictures). Granted, that was a large woman, so 10.5" is a smaller percentage on her than it would be on me. But I'm never going to get skinnier, and I'm very likely to get wider. So why not make the kilt say, 4" wider than my measurements, and put the buckle where it should be for my current weight?

My hips are 4" wider than my waist, and I already know that when I put on weight, my hips remain roughly 4" wider than my waist. A hidden pleat is sometimes added for adjustments later. But why not skip the hidden pleat and add some extra real pleats instead? Then I don't need to take the kilt apart if I gain weight. I can just adjust the buckle strap locations.

The only significant reason I can think of for me to NOT add extra pleats is because you want the underapron to show if you're in a situation where the apron is splaying open. But I truly don't care about that. People can see extra pleats instead.

The benefits of adding extra pleats (being able to continue wearing my kilt) seem to vastly outweigh negatives (seeing extra pleats when splayed and the apron/pleat ratio being skewed when getting wider). Is there anything I'm missing?