Chase,
I am guessing that you mean the spring support changes from say a Grinnell Figure B-268, increasing in physical size to a Figure 98 with double stack spring or even a constant support. This results from the load variation exceeding the 25% limit criteria for the spring selection. Another way of viewing it, the spring travel may be exceeding its design limit (Fig B-268 physical limit of 2" maximum travel, but 25% variation will result in closeer to only 1+" usable travel). If you have 3" of piping deflection, then constant spring suppport is needed unless you can allow greater than 25% load variation.