It's to do with oils and sugars used in the sauces. I'm guessing purely based on syn value you're talking about the teriyaki one? (That's one of my favourites!)
I've also found that the John West ones are all syn free so if you can get those, you're onto another winner
I've only found them in Sainsbury's, although admittedly I don't use Asda so I've never looked there.
Sent from my iPhone using Tapatalk