Perhaps it's your playstyle, but if I were you I'd abuse AS The-O's no range disadvantage.
SI's boomer may not be that powerful, but it sure doesn't hurt to use it a lot more when facing him, also you can wait for him to come to you instead of charging head on - after all AS The-O NEEDS to charge or he can't damage you at all, and with that skill of him that add amount of boost, which do you think is better for the following option?
1. Not using range attack, charge at him, which saved his boost and wasted yours, you then are at a disadvantage
2. Using range attack to slow and wash his HP a bit first while stay at where you are (but be alert), which he wasted more boost while you hardly lose any.
I dunno what's other take on this, but this is at least what I'd do :3