Gosh, I don't know. As I mentioned I DO have these on mine - and I don't remember such an issue, or if there was it only took a little trimming.
There again, as I mentioned, I don't have mine set where I come anywhere close to having them set so they go to the "end postion" in either direction - and, at least part of the reason is that the hardest one can be on a servo (and wear it out the fastest) is using it/setting it so that throw to either side extends all the way to it's end position (or full throw).
Here again, as I alluded earlier, some people have had issues installing OTHER brands or models of servos in the RC18 - and the fix was to modify the servo mount by trimming a little away from the mount on both sides allowing more room for the servo and/or it's movement front to back during installation.
BUT, my feeling is that you're expecting the throw to be total (or full) in comparison to how it was stock - and it's just not needed. Set the transmitter, and put a mark on it, that is at full throw - and then put everything together and give it a go. My guess is that you'll still have plenty of steering, and might even need to dial some out.
