The springs in the standoff subassemblies should be compressed to 9mm or 6mm of length, depending on what build platform you are using with your 2014 Series 1 machine. Use 9mm for 1/8" thick lower bulid plates, as the extra thickness compresses the spring further when the build surface plate + glass is inserted. Use 6mm for thinner 1/16" thick build plates that shipped with 2014 Series 1 Beta machines.
Set the standoffs to 9mm (approx 11/32", or otherwise) of compression length as measured between the low side of the fender washer and the upper side of the first nylock nut on the M4 screw.
This results in about 4lb of force exertion per standoff when the 1/8" thick build surface is inserted into the standoff assembly, and around 15lbs of force total with 4 standoffs holding the build surface lower plate + build surface glass.