Valve lash article
The heavier the valve springs, the more cam deflection is present. Going to the Mopar 90 degree system helps reduce inconsistant measurements in some cases.
If i am off more than 5 to 10 degrees i see different amounts of lash.
For shitz and giggles i measured lash all the way from close to open to see how much change there was. Consistant .005 difference was observed around the base circle. 300 lb seat, 860 open