The Fox provides 50% bonus to tackler module effects. However, the actual bonus to engine suppressors is much less. Might be done on purpose for balance reasons, but should be stated correctly in the ship’s description then.
Mk.I - 44% -> 55% = +25%
Mk.II - 50% -> 60% = +20%
Mk.III - 58% -> 68% = +17%
PS: The target painter is the only tackler module bonused for the full 50%. The inhibitor beam receives no bonus at all from the ship.