The April 2009 Update has lowered the TP per upgrade. It is no longer 60% and is instead the 40% mentioned in the tooltip.
Removed: Each level upgrade is in fact a 60% TP bonus, despite what the Merit Description says. Each <pettp> is worth ~1.66 Damage. Each Avatar Magical Attack Merit adds ~16.6 damage consistent through out TP range. Blood Pact Damage appears to 'cap' at 300% including 'Bonus' TP. Source  --Tannlore 21:26, 17 April 2009 (UTC)