Kobuntura (IIRC) have +1 shields to their ships, regardless of mounting or not a shield in the ship. It's nice early game but irrelevant against plasma (or fighters).
I suggest a species trait that gives +20% (rounded up) strength to any mounted shield part in their ships, per level of the trait (if bad, rounded down). Final values for each shield depending on trait would be as follows:
Doesn't seem an OP trait since shields can always be countered with bombers/fighters.
Do you like it?
Alternatively, the Shields trait could be about part cost, so that Good Shields reduce shield parts' cost by 33%, Great by 50%, Ultimate by 67%. But I like more the above version.