It used to be if you entered in as a group, then you (or someone else with a group) had the chance of being the group leader. However, I believe this was changed so its pretty much just random.

Your best bet (beyond the change the macros around) would be to ask nicely for leadership a few times till you get it (don't spam the leader) or ask that he put all your characters into the same group.

It also helps if you tell them what group your in when asking for leader, helps them avoid having to look. Example: /tell legolaselflol Hey I'm in here with a team of shaman, can you please give me leader (i'm in group 2) or if you want, you can move my 3 other characters (names..) into group 2 with me.

something like that. Also avoid sending the person a tell right at the start since theres usually joining spam (like in AV). Doesn't hurt to wait about 10 seconds or so to make sure the leader sees the tell.