Trouble is, reading the above, can any improvement be achieved?
You have two options:
Accept what you have contracted for
or
Challenge it.
To challenge it you need to ask the installer to show you how his chosen system will perform correctly with the 2 MPPT's that he said were nescsarry in the configuration that he has designed, adn give him the chnace to reply fully in laymans terms.
So there are 4 possible solutions
1) You've got what you've got.
as there are two areas of installation with different orinetations, in a first class design, they should either have been
2a) on Seperate MPPT's - (dual tracker)
HOWEVER: The chosen inverter needs to be able to cope with only 2 panels on that one string - I doubt this is the case. If it is fine, ask the installer to show you, else you have 2 other solutions, both of which require you challenge the installer further, wether you have legal contractual grounds to do so or whether caveat emptor applies, I cannot comment.
2b) Possibly two inverters, though whether there is one small enough for the 2 panels I cannot say, the Soladin 600 is about the smallest, though two enecsysy micro inverters (see below) would do the job. plus an inverter properly sized for the main roof.
If you decide to challenge the installer further, then the two best solutions are
3a) Micro-Inverters. Enecysy or Involar - you have one inverter per panel, so gauranteed no mismatch.
or
3b) SolarEdge Optimisers, these are attached to each panel, and effectively give each panel it's own MPPT, without actually being and inverter, so with the appropriate interface, they can be attached to any inverter (obviusly it would be best if it was a SolarEdge invertert, that way you don't need the interface.
That's really it unfortunately. You need to give your installer the chance to fully explain how it will work they way he has designed and installed it. If there are some compromises in the design these should be reflected in the output figures (kWh / annum) that you were quoted. If those compromises have been included there, then that's the end of it (legally)