those ranges are not solid and can change day to day based on the weather. those stated ranges include multipath and static. the antenna has to be in a very specific spot and orientation on the fringes. the buildings here have wood siding but have steel mesh reinforced stucco behind the siding so i get directional and reflective attributes because my part 15 is mounted outside in a whether proof box it gets bounces and reflections from the siding. i think what might be happening is the little patio alcove the tx is in is acting like a small vhf sturber curtain causing directivity of the signal toward the other two building across the way which is then reflecting the signal in the other direction because my signal does not go much behind those two buildings across the way but goes much furhter in the opposite direction behind my building and away from those other buildings. there is no way to get a good true F/I reading here because of that issue. if these buildings were just wood and not giant faraday cages or if this thing was in an open field i think the range might be a little less. my decade does about the same range as as the B.V. / Waio transmitter.
TWO of my certified FM transmitters do what I need...
The Whole House 2.0 gets signal 11-feet to a C.Crane Radio Plus receiver which is used for audio editing at 101.5 MHz.
The Scosche FMT4 gets signal at 88.9 MHz from one room to another to transfer vinyl discs for digitizing.
But the C.Crane FM transmitter at 89.5 MHz is plagued by multipathing in the 20-feet from here to the back room for audio link to the AMT5000.
I am thinking that vertical antennas might not be the best for indoor FM.
The human body is vertical, and competes for vertical space with the FM signal.
Also, consider that rooms are wider and longer than they are high, which seems more conducive to horizontal FM transmission.
So long as the directional nature of a horizontal antenna is accounted for, I am of the unproven belief that my indoor FM antennas should be horizontal.
Comments welcome, I will be reporting on test results.
Now I have to design a way of physically locating the transmitter/antenna for horizontal.