Not to dispute your statements, just curious ('cause I don't know):
The width of the 'new' lifter's flange doesn't come into account?
If the diameter is wider across the face (by 'x' mm), wouldn't this add a little more duration?
... or is the overall length of the lifter shorter (by 'x' mm) to compensate for the wider face diameter?
What about the push rods? ... are they stock length, or sized-to-fit?
... and, what rocker assemblies are you running?
I doubt very many components in your engines are off the shelf 'stock'