I did the math and calculated it out. A level 64 character should be able to group with a level 96, according to the character level x 1.5 rule. I just tested this out, but found that a level 64 character was unable to gain party exp when grouped with level 96 characters. Does anyone have any idea why this is, or what the correct math is for this now? Thanks in advance for your time.
In addition to the 1.5 rule, there is also a cap of (I think) 30 levels' difference, so you need to be 66 to group with a 96 toon.
I didn't know about the 30 level thing but it appears true. It's 65 for 95 and by the 1.5x rule a 67 should get exp with a 100. However, I tested this and the lowest level you can get exp with a 100 is 70.