This post sound a lot more like one person thinking out loud, or two people having a conversation in such a way that they are trying to teach something - a lot like a infomertial.

The bottom line is - who cares.

.1 watt or 1 watt - the antenna the OP showed is either for 400 something Mhz or 900 mhz.
Until the neighbors complains - you can do what ever you want.

A local ham once told the story of a neighbor that had a baby monitor that operated on 50 something MHz.

To this ham - 6 meters was sacred.

To have to listen to some screaming baby day and night was intolerable.
Especially since these people lived on Mt Morenci road near Ridgeway PA and the elevation there reaches somewhere near 1900', the average terrain being only about 1400' - the baby monitor acted a lot like a 50 watt transmitter because of the height gain.

When they complained to the owner of the baby monitor, those people just laughed and said that it was a problem that the manufacturer should address, not the owner. So the hams made some tapes of the couple making love - which came over the baby monitor loud and clear each night and passed them around the community.

It wasn't very long after the couple found out that they were going viral that they got rid of the baby monitor.

The output of the transmitter has a lot less to do with the range of the transmitter then does the location and size of the antenna.
the problem being that if the radio transmitter was 400 mhz you would have some loss in the coax between the transmitter and the antenna that would negate any gains to be had by putting the antenna higher or outside.

If the radio transmitter was 900 mhz, now you have a big problem - where the loss in the coax is so great if the coax is more then a couple of feet long that any gains you could have are lost in the coax and unless you properly match the coax, the heating it might cause inside of the cheap $50 transmitter might be enough to burn it up.

Hence if the transmitters frequency is high enough, it will solve its own problem..

A FM broadcast transmitter in the range of 88 - 107 Mhz wouldn't really matter. I guess this is the point that I am making.

I have read several articles of night clubs - especially around the Cleveland Ohio that took it upon themselves to modify a FM transmitter that would normally have a range of about 1000' and modify it so it could be heard 20 miles away.

When the complaints were registered by the legal owners of the frequency, the FCC stepped in and removed the transmitter and gave the owners of the club a big fine. A month later a even bigger transmitter was found on the premises and another fine was levied. Two months after that, another transmitter was found on the property - which leads me to believe that the transmitter that the FCC found was the one that the club wanted them to find. The second transmitter was an alternate transmitter and the third transmitter was the actual transmitter. By the third fine, there was no way that a club - even in Cleveland Ohio could take in more legal revenue then it was paying out in fines. Oh and did i MENTION -the dancers wore no clothes.