A friend of ours wants to secretly buy her husband a kilt. However she (and I) am unsure of what is the 'best' size to get. The kilt will be a relatively cheap 2nd hand kilt from ebay as a starter kilt to get him in the kilt mood

What I am unsure of is the waist size for the kilt as he has a large stomach, 46", but his trouser size is 38-40". Should I look for a kilt which is close to his true waist size (46") so that the kilt will go around the stomach or should I look for a kilt which is a bit smaller so it can be worn lower and the stomach sit a bit on the top of the kilt?

Appreciate your advice