First, questions about FIRST rules should be posted to the
FIRST Forums - at least if you want an official answer. As you may have noticed, the first response to your question gave the answer for FRC, where you asked about FVC.
That said,
this exact question was posted to the FIRST FVC forum not too long ago, and the answer is that the antenna (and anything else) has to be within the 12 in. height requirement.