No, your cable bundle size is not limited. The factory and 3rd-party testing that is done for Category 6A Alien Crosstalk is done in a “worst case” 6-around-1 configuration (7 cables). The “one” cable in this configuration is called the” victim” or the “disturbed” cable. This is the cable where the noise is measured. The other 6 cables are called “disturbers”. They are held in close and constant proximity to the “victim” cable; typically by being Velcro-tied every eight inches for the full length of the run being tested.
Cables may be run in virtually any size bundles; 6, 12, or 24 are typical bundle sizes (because those sizes typically match up with the quantity of patch panel terminations). Field Alien Crosstalk testing should be run on the whole bundle, so for a 12-cable bundle the alien test would be an 11-around-1 configuration. The field test results for an 11-around-1 would typically be expected to be much better than the factory 6-around-1 test configuration, due to the random lay of the cables in the field installed 12-cable bundle vs. the tightly-bound nature of the factory test cable bundle.