Thanks Old Smokey for your time and interest, but I´m afraid that this answer is quite simple.
Your opinion might be valid when talking about wing anti-ice or air conditioning bleeding, in both cases EPR and gross thrust are reduced.
But when using engine anti-ice EPR, as well as Gross Thrust, remain constant so what really decreases is the Ram Drag created at the engine air intake (not the combustion chamber) cause of the deceleration on the free air stream, as a result net thrust is increased.
Anyone out there could give any other reason for this?
REGARDS.