In the latest manual on the website under heli installation it says (about the second antenna):

'The overall length of the antenna should not be less than 1 metre, no problem if longer'

It doesn't seem too specific to me. The manual does not caution against what you have suggested.


If you are really worried about it, you could always cut a couple of inches off the whip to maintain the original overall length.


EDIT: you can download the manual from the website if you need one.