Based on my experience I'll make the following comments.
1) parallel panels or strings should all be the same or close to the same string voltage, each panel or string can have different current rating and the MPPT controller will accomidate.
2) All panels in a series string should have the same or similar current rating (power). The string will be limited to the lowest current output of the panel in the string.
so based on your setup adding a 100W panel to a series string is not a good idea your limiting the current from a string, nor is adding a 200W panel to only one string, now you have parallel strings with different total voltage which the controller will likely have a fit with.
Now what to do? well you could add a couple or maybe 3 200 or 100W panels in series and run them to another MPPT controller and parallel controller output to the battery. check and see if the system allows parallel controllers
this is basically what I have on my trailer. roof has 3 200W panels in parallel to a Mppt controller (Midnite solar) and up to 4 200W portable panels I can use wired to another of the same controller. with the midnite solar system one controller is the master (roof) and the other the slave (portable). Master determines which mode the system should be in, bulk, float etc. and sets the slave to the same setting so both controllers are giving the same charge profile.
Depending on how far my portable run is and how much (or little) shade panels see I wire the portable panels in series or parallel, or a series parallel combo.
Have used this for years and it works great.
