Yeah, that's really op. Especially for 50pts. A 15cm radius and one column shift would be more balanced. Otherwise this would make your entire fleet damn near invulnerable.
Another solution would be to make the ECM a type of "attack". Range of 45cm, pick one target (Defence/Capital ship/Escort squadron fully in range), that unit makes a Ld test. If it fails, then it suffers the penalties as given. Still powerful, but has a chance to counter the ECM.
Hope that helps.