I tested my pro in various locations but it will not cover the house, I have changed the radio settings to "Transmit Power" to High in the AP configuration but this made no difference. I am testing this as if it is ceiling mounted, I can't find a setting to say whether it is ceiling or wall mount so it doesn't care?
Are there any other settings I missed to help with coverage?
I may need to order another unit to go with this, maybe the LR version.
Look at replacing the antenna's rather than anything else. i use a directional antenna (patch panel) on one of my antenna points to reach a single direction over a long distance. Routers are limited by power output and there is nothing you can legally do to change this. However changing the antenna can seriously increase your range.
Like Randall says this was always going to be the problem. Long Range or not the power limitations and the frequencies that WiFi operate on will always hamper you. Of course, buying a different antenna while giving you longer range might not have covered the width of your house, causing its own issues.
As myself and many others guessed one AP was never going to cut it but it was worth trying to save a little money. Whether you need a "Long Range" one in addition to your current one only you can tell but don't expect it to work any better inside your house.
"Long Range" only refers to the outside best case scenario. Having a LR and regular AP in a house next to each other you'll likely only see the distance extended by 3 or 4 meters.
In addition, while you're testing the range and coverage are you doing a speed test? It's fair enough that you might think you just need two to "cover" the house but whether that's a usable coverage is another question.
Of course, this is only something you can confirm. It does sound like you've got particular issues that might be compounded by pipes, aluminium lined insulation or solid walls that without a house survey it's hard to recommend exactly what you need.
Saying that, you're on the right track with the Unifi kit. Consumer grade stuff when you start extending off extenders is asking for a mess of problems. Starting with one Unifi AP and getting more it can only get better.
P.S. They are directional with the intention of being ceiling mounted. They can be wall mounted just be aware that the signal will drop off rapidly if you were behind it.