FX hammer spring adjustment question

I can see all the different theories/explanations etc,on this subject, but then please explain why does the fx impact have a adjustable valve anti-bounce/bumper device?





Please point me in the direction of this literature/ information. Makes sense if the valve/poppet is bouncing off the back wall causing it to close quicker past a certain point.
 
There are several very good videos on YouTube that address this issue specifically to the FX Impact Ernest Rowe for one but there is a guy called 

MeatHeaed Marksman who does an great job with simple diagrams and explanations. The requirement is that you own and know how to use a chronograph. FX has a new Radar Chrony that has gotten good reviews and costs $200. Multivariate equations require time spent . GOOD LUCK