Had a day off today after yesterdays exertions and was out with my brother who is visiting this week. Both aircon units are now controllable via smart phone and I set a timer last night so they both came on today at midday. SWMBO came back from work mid afternoon and texted me it was bloody hot at work but the house and even upstairs was lovely.
On my return I found that it was too cold downstairs as some of the cold air from the upstairs unit was adding to the cold air downstairs so I have altered the temp and I set the downstairs unit one degree higher (lower power) than the one upstairs and that seems to be just right.
The unit upstairs is high over the stairwell and we left the bedroom door open and another spare room closed. I just checked the temps inside our opened door bedroom verses the closed door spare room which are both upstairs.
The closed door spare room feels hot and humid, temp 26 degrees, so is like what out bedroom normally feels like in these hot conditions.
The opened door bedroom is a comfortable 21 degrees, so it works as I hoped even without fitting aircon in the actual bedroom which would have been difficult.