An inch or so should not hurt all that much.
If it were cut off at the base instead of the top, then you could have issues.
A rule of thumb length for am & fm rc radios is 20". Most rx antennas on rc's are within an inch or so of that.
While it's true that antenna length is dictated by the frequency being used, rc systems are designed to operate over a range of channels (or frequencies) without having to retune the transmitter or the reciever. Hence they don't have to be an "exact" length.