I would probably run scutum at 30cm myself, as for sparrowhawk I don't really see it having a strong ratio to be too problematic, because most IN players play very little ordnance, and three together is hardly game breaking. With the eagle at 45 you have 2 strong options for escort AC, depending on your fleet lists. My armageddon list, for instance has only defensive escorts, so I would run 2 eagles and 3 falchions in my defensive escort squadron. With 3 torpedo markers and 2 AC it would be quite good at taking down AC, and although 13 battery is not incredible it should be able to account for some more AC if need be.