My understanding of the IG plus inverters is that the use the Fronius MIX concept. There are 3 power stacks, one per phase. The inverter starts up in the morning using the one with the least logged run hours, then the next, then the last one as power increases over 1/3 of the power output. The idea being that this means the stacks are running efficiently (top end of their output) and the run hours are kept to a minimum.
The downside to this is that phases are not balanced, and you never really know which phase you want to be using power on.
This is all done with 1 MPPT tracker.
I believe you can also set up to balance across phases, too, if you wish.