Generally:
If your BST is 1-99, your pet called via Call Beast or Bestial Loyalty will be:
0-6 levels below the beastmaster job level, but up to the cap of the jug pet.
If your BST is 1-99 and you have Monster Gloves +2 and you have 5/5 Beast Affinity Merits:
0-2 levels below the beastmaster job level, but up to the 10 levels higher than the cap of the jug pet. (2 for each upgrade to beast affinity).
If your BST is 99 with a iLvL axe and you have ankusa gloves +2 and 5/5 Beast affinity
Your pet is the level of your mainhand axe up to 10 levels beyond the cap of the jug pet.
It's all explained here:
http://www.ffxiah.com/forum/topic/45...ter-compendium