maybe Will said that, but I don't know if there was a specific context.
Sizing is as follows:
PV minimum array = the minimum array size needed to generate your minimum daily kWh consumption.
The daily CONSUMPTION is typically divided by 5 to approximate your array size.
If your battery is lead acid, then division by 5 is more appropriate because lead-acid needs to be charged at a 10-20% rate to ensure you don't damage them by charging too fast or too slow.
MPPT are rated by output current. That one is rated for 80A output. That means it can deliver a maximum of 80A @ peak battery voltage, so about 80A * 28V = 2240W... and those claim a PV rating of 2000W, so that's pretty accurate.
You have 800W, so you could clearly add more.
That MPPT is limited to 145V maximum, so you need to stay under that. With an input voltage of 90, it sounds like your existing panels configured properly (What is your panels' Voc value?).
You could easily triple your array with the three strings in parallel, i.e., 4S3P and have 2400W available, though it would never deliver over 80A output. You will be slightly over-paneled, but this shouldn't hurt anything.
If lead acid, 9.2kWh = 9200/24V = 383Ah, thus your batteries are charged most healthily between 38.3A and 76.6A, so maxing out your array should be fine.