This might help
-Limitation of mechanical geometry , roller , flt, or even mushroom tappets , when mechanical geometry does or does not exceed its limitation, also with these examples the same lobe center seperation would have different valve over lap values - meaning there would be different dwell time and acceleration lift/close at the valve. Something else to think about too much lash will crash the valve into the seats , meaning more bad harmonics for the valve train - [just a general statement of ideas and thought maybe will help maybe not]
-If one man thinks hes better than a another he will never hear a wise mans words- Marco