I now understand the empty plots I was creating with the T6 event type cut. Kalyan showed me that (D.evtypebits&1<6)==1<<6 gives the correct plot. I was naively using D.evtypebits==0x40 and getting no results. The reason is the following:
D.evtypebits==1<<6 will give you T6 only if NO other triggers coexist
(D.evtypebits&1<<6)==1<<6 will give you T6 whether or not other triggers coexist
Bob Michaels included this in his explanation in entry #330820, so I definitely should have known better. The condition for T6 is that of T4 + right gas cherenkov. So for every T6 there is a coexisting T4. Therefore you must use the condition that you don't care if another trigger coexists.
Thanks to Kalyan and Bogdan for helping me figure this out.