How to measure myself for a kilt; suck in stomach or no?

[User]

Almost every source I've read says to keep your stomach natural when measuring yourself for a kilt. Don't suck it in, don't push it out.

But in this video by kiltmaker Robert MacDonald, he says:

Now what I'm going to do is I'm going to ask him to suck in as hard as he EVER CAN, and then I mark it with chalk.

https://youtu.be/da5wOJViszQ?t=82

Later he says:

We ask the gentleman to suck in as hard as ever again, and then we do it up.
...
I'm doing it a little tighter than is possibly comfortable. But, over time with a finished garment, when he's wearing this, the kilt is going to shape itself to him because we've tailored it to be a section of a cone. As he wears this kilt it's actually going to get more comfortable as the kilt shapes itself to him, and to that end this very tight strap is not going to be uncomfortable in the future because it's going to shape itself.

https://youtu.be/da5wOJViszQ?t=265

It looks like he's setting the smallest size, with the buckles allowing for growth only.
Conceptually, that seems fine. I don't expect to lose weight over time, only to maintain or gain it.
But I've never seen anyone measure for a kilt like that.
I'd like some opinions on it.
Is that style of measuring only for completely bespoke designs, or would it still be good for more off-the-rack kilts that only use a natural waist and hip measurement without a custom fitting?

I have about a 3 inch difference between sucking in and not. That gives me pause when considering how I should be measuring myself for a kilt.