It is true that with the buck converter, MPPT controllers do better on "same" voltage for panel and battery than when bucking from higher. PWM is always 12-12 or 24-24. MPPT is also 12-12 or 24-24, but is often 24-12 or more.
When I did my 24v battery with 24v panel test, one thing that came out was the 60 cell panel was able to raise the 24v battery bank to 30v max (like 15v with 12s) so it was able to do a recharge ok, but would be unable to do an equalize if you ever wanted to do that.
With 36 cell 12v panels in series, two is 72 cells, which ought to beat the single 60 cell when trying to do equalize level voltages on a 24v bank. There are 72 cell singles, but 60 cells are very common.
My Eco-Worthy 20 amper at 42Voc input limit would be over limit with two 12s in series at 21.9 each, but my Tracer can do 90-100 Voc so there is another factor to consider if you are looking at your options. A single 24 can be less money than two 12s though.
The Eco-W has adjustable voltage settings while the Tracer has a fixed charging profile (which is a good one for many situations) unless you spend more for the adjustment gizmos.
Lots of factors to consider with solar.
