No idea. ECA may have been Protoculture idea so the Vajra may have been influenced by Protoculture. Since the red Vajra seem to have a much more powerful core, it's probably without doubt they have stronger ECA, which is why they seem to be more resistant to missiles and other anti-aircraft weapons. Short of getting in close for melee combat, high velocity ammo, or several shots from a particle weapon, you'll probably need to use a high yield explosive to penetrate its shell.