Does your x-breaker have the G10 tip?
I wouldn't touch the G10 tip.
If you want to try a flattened tip, try to get a shaft with a leather or phenolic tip, and test it out.
I think using a flattened tip will cause more miscues if you are using english.
I have played Carom ball in Korea a few times, and their house cues have large, hard flat tips. They use these heavy duty, metal files to condition the tips.
I have noticed when using these flat tipped cues, that aiming too far away from center will produce a lot of miscues. With a rounded tip, you can aim farther away from the CB center, with less miscues.
That's just my experience.
P.S. I have the x-breaker with G10 tip, and haven't had any problems with it. I've performed power breaks using top english, bottom english, center hit.....and no miscues, or horrible CB control, as of yet.
I just usually don't get the CB to stay in the middle of the table, like I want it to, because OBs are flying all over the place, and usually knocks the CB around.