Magnum head question with +.100 longer valves

You lost me!! I know you know a bunch about engines, but how will lower valve height help bind? I'd think it would be the other way around? That is, won't a taller valve allow for more room with an extended spring, when valve seated?
1st part, thanks for the reply. My writing out my thoughts needs work. The stock height valve or keeper grooves would just let the guy start over and we could use a known spring.
The free length is not the issue it is that it gets to coil bind at .470 when lift is .535 after I rechecked the math. Still not enough room.