i would worry more at this point as to why the servo moves 1 way and not the other and go through the head and make sure everything is set up correctly and balanced before anything else happened . and mode 2 ? do you mean idle up mode? if the gyro and tail servo are any good it should already be set wether your in training mode or 3d  in mode 2 "idle up" the head servos will move farther usually down more to achieve say a +10 - +13 through a -10 - -13. but thats all set in your pitch settings in that specific mode. ofcourse i dont know what kind of adio you have bu all of this is done in the settings in say the dx6i 7 8 and or futabas,jr, etc. blade 400 bible you wont go wrong learning how to set  your head up etc