1, Floor Finish – The resistance of your floor finish insulates the UFH system. So basically a 10mm tile will perform far better than say 25mm wood boards.

2, Flow temperature – The temperature of the water circulating through the pipe affects the performance of the system. Looking at your post it looks like you are using a boiler with a flow temperature of around 40-45°c .

3, Pipe density – The density of the underfloor heating pipe plays a large role in heat emitted per square meter. For example 100mm pipe centres will perform far better than 250mm.

And as for pressurising the underfloor heating pipework your correct. There have been occasions where the UFH pipe has been nicked and trades try and hide any damage they have done. That’s until a 2 meter high jet of water alerts everyone nearby to the damaged section.
It can be very expensive to find and repair the damage after the screed has gone down.
I recall one project where a clumsy joiner nicked the pipe 6 time’s and at £100 per repair the owner was less than happy.
Good luck with the install guys.