Page 20 of the short user guide discusses mounting, specific to the EasyMini and baro . Page 10 of the comprehensive guide discusses the TeleMini, which is also Baro only and it says "Since there is no accelerometer, TeleMini can be mounted in any convenient orientation."
While it does not specify the EasyMini direction it does discuss light exposure specific to the baro sensor as well as the importance of the baro sensor being able to "breath" so don't block it with foam etc.
My take on this is that you are good to mount it this way, assuming it does not violate the other warnings.