I think you'll be able to larger than that.
I use a medium cage X9 mech with an 11-36 mech no worries.
Just looked at the Sram website and it says the mech will work with up to a 36 tooth cassette. They define the short cage as for DH use but I think that means single ring be ause the medium cage is if a 2 x 10 set up.
2015 Stanton Ti Switchback
2006 Specialized Demo 8
2013 Specialized Allez Sport
1999 Santa Cruz Chameleon
1994 Cannnondale Beast of the East (rebuild still in progress)