I think the only Liberian that can access Divination discipline is Tiggy himself, so you may have to let the other Liberian roll on telepathy tree.
Actually,
IMHO, I think the perfect timing in divination is quite strong to be put on grav cent, as it let that weapon becomes ignore cover and Ap2, any monster lack an decent invunerable save would be killed.
If one of your Libby get invisibility, he is not necessary to be stick in the squad, because it is a blessing grant to a unit within 24inch.
If you footslog the cents, I think you may consider try to get Levitation from telekinesis discipline.
IMHO, that may make your mini Death Star more scaring, since your grav cannon now get 42 inch threat range. (6 inch movement + 12 inch flying + 24 inch shooting range)