I've been trying to find this for ages! To no avail. I really struggle with my hexb, I tend to find if I have it then I gain or STS.
I tried tricking myself into having it by having the scan bran coffee cake.. 5 scan bran used.. 5 scan bran hexb per day. That meant I could eat a whole cake a day and be 100% on plan!!
At my group everyone uses 42g of Morrisons puffed wheat, I add sweetener as think it's bland without and eat it often as a B choice and always Lose every week. Morrisons own make is only £1.09 and it's gab for quickness too!
I'm sure that the 28g is where you need to add the extra scan bran but I'm sure that if you have 42g you don't need to scan bran. In our books there are certain cereals that say '28g + scan bran OR 42g' so I've always gone for having 42g and not the scan bran as I don't like them very much!
If SW say that you can only have 28g then maybe that is what we should be doing but most people I've spoke to have 42g and lose weight most weeks!