Sorry just figured a better way to explain your answer domum. If...

Sorry just figured a better way to explain your answer domum.

If you consider the HRZ as a house with 3 rooms and the HUE as a seperate house.

Now consider fraccing as renovating adding to that house each room can be expanded only so much before it is destroyed.

Now at a certain pressure consider that rooms 1 and 2 will withstand the work and hold up strong but if that same pressure is applied to room 3 it will be destroyed.
Now lets assume that by adding this pressure we could add 100sqm to the house but we would leave room 3 say 50sqm unused . It would then come down to trying to aquire the most amount of usable sqm while not destroying the building in the process.

Now when this takes into account the HUE treat that as a second house we could possibly join to the first or use seperately.