Leaking through diaper at night

downtown80

DS has leaked through his diaper the last few nights. I know that generally the recommendation is to go up a size. He's wearing a size 1 Swaddlers.

Forgive me for sounding dumb, but is it normal for his leaks to happen at the top of his diaper above the bum and near the hip? He is a back sleeper. Diapers are just pee. And it's only been about 3hrs since his last change...so not that long. He goes that long or longer during the day without leaks.

DD never had leak issues, so I'm just confused. If anything, I would imagine the leak would be lower by his legs.

Thanks for any info!