the controller monitors the battery state and will lower the voltage as needed to charge to the parameters you set. By dropping the voltage, the current will drop as well. My controller allows me to set the bulk rate, absorption rate, absorption time and float voltages among others. These settings are found at the battery manufacturer site.
Don't be upset if you never see 40 amps output. I understand mathematical you could see that amount of current. You would have to aim the panels perfectly, at the right ambient temperatures, perfectly clear skies and, here's the biggie..a dead battery. Yep, a mppt charge controller charges based on battery state. If it ain't drained, it won't put out the current. My system should max out at 25 amps. With my batteries around 67% (-71AHr) the charge controller only put out something like 16 amps. The battery was at 100% by mid day. I added load to panels by turning on lights and fans to get it to around 19 amps. I can't my notes so don't take the numbers exact. The point is, the controller will only put out what it determines the battery needs.
2000 Cherokee 29BH with 6V batteries, LED lights & 400 watts of solar power, flipped axles and raised. 2007 Tundra 5.7L DC-LB with lots of mods. C-co, 8/158th AVN Maint.