Hum... Looks interesting, but one question: 20 OP difference compared to what?
In the above example, 30 - 10 = 20.
30 is the S-Mod Compensation hullmod's upper threshold for
capital ships (5/10/20/
30).
10 is the usual cost for Advanced Turret Gyros on a
capital ship (2/4/6/
10).
So the difference between the two is
20 OP.
Finally, multiply that by 75% and you get
15 OP refunded.