Metris rear spring question??

[racer21]

I see some builders add a 3 inch tall bucket to the rear top spring pads and run the 16 inch springs and some builders don't add it and run the 13 inch springs, Is there a specific reason for doing this or not doing it,Thanks in advance

[floppyfoot]

We use a 16" on the LR and a 10 1/2" on the RR.