Transverse-mounted ribbon tweeters?

Has anyone seen a speaker with ribbon tweeters that are transverse-mounted? This would make the directivity pattern vertical instead of horizontal, which in almost all cases would be undesirable. However, if you were installing drivers to target one specific listening spot and the only variable was the listener's height, then a vertical directivity pattern would be more desirable I would think. Does anyone know if there are any detriments to installing and operating ribbon tweeters on their side? Are they sensitive to gravity? Thanks in advance,