An extra 1 to 8% is the typical range on a TAP link, on top of your standard creator commission.
Why the boost varies
The number is the brand's, not Soco's:
Each brand sets its own TAP campaign commission boost, and Soco negotiates the best rate it can get for its users.
Soco passes the creator portion of that boost directly to you.
The exact increase depends on the product and the brand's offer at that moment.
Soco offers links at the same or a higher rate than the one it can see. It can't see a rate you agreed privately with a brand: Will Add All replace a higher rate I get directly from a brand? Your standard creator commission doesn't change: Does Soco take any of my commissions?
Next steps
Where those links come from and how they behave: