GrandClick is 50% refback.
80% should be per referral click (not sure if they changed it). Check their upgrade page and Standard/Free membership.
What also can be the issue: Refback is counted only from Standard/Sponsored ads (those ads that we get referral commissions per click from), not from all your clicks.
GrandClick is a site of Lenca (our other admin), I cannot look there myself so correct me if Im wrong.