If, theoretically, there was a mod that made it so that taking Glass Cannon reduced your base Recovery AP prior to the GC buff being applied, how much of a reduction would be necessary for it to be balanced?

Like if the reduction were 3.5, then with 5 speed + GC would equal (3.5 base + 5 speed - 3.5 GC penalty)*2=10, while without GC and 5 speed it would be 8.5, with the difference increasing by 1 with each point in Speed. At 10 speed it would be 20 vs 13.5 for example.

Or would it be more balanced if GC were to multiply AP recovery by a smaller amount, like 1.5x instead of 2x?