Stock Ford glass is 70% so you have to take that into account when you tint.
Here is the formula:
glass% x film% / (glass% + film%) = real%
Example: Llumar CTX 30 is actually 31% so if you do the math...
31 x 70 / (31 + 70) = 21.5%
Just for a reference, Ford dark privacy glass that you find on the rear of vans and pickups is 17%-18% so you would need a film in the low 20's to make the front door glass match.