It that's TFA's Ry4 Double, then that should be plenty strong enough to taste, and fine right after mixing. I vape Ry4-D every day and mix at 8%. Something else is afoot. First eliminate any equipment issues by trying another
juice.
Then shake your flavor vial and smell. Do you get a faint smell of caramel? If not, then let your dad try this. If no one smells anything, I'd request vendor replacement. If you can smell, then probably something wrong in your mix. Did you mix .45ml rather than 4.5ml? Anybody call when you were measuring and mixing? Are you measuring with syringes (or scales) Also good practice to shake your flavor vials before mixing.
Anyway, try mixing another small sample (okay without nic) and post your results.