True, but as a result the gain of the -1F antenna is a bit lower. For typical deployments (especially with the AP-13x which is less sensitive to the issue than Ap-9x or AP-10x) I would recommend using -1B. If the expected interference from cellular systems is quite high (AP's positioned within a coupld of m of cellular transmitters/antennas), -1F would be the better choice.
Thanks,
/Onno