Mantaray driver with a stacked R020 resistance? What I can remember from having seen it in AliExpress somewhere, the Mantaray driver you are speaking of uses an R015 sense resistance, and claims up to 7A of output. With these figures it is easy to infer that maximum sense voltage is Vsense = Istock × Rsense = 7A × 15mΩ = 105mV.
Technically speaking it is a linear driver or regulated variable load driver. Uses a MOSFET or MOSFETs as variable resistors, and a sense stage to “feel” the flow of current and do its job.
These drivers are set for a particular current. When current goes through them, they sense it in their MCU thanks to its sense resistor and operational amplifier. This allows them to regulate in a sort of conscious way.
The key with these is to adjust the sense resistor value properly, if required. When you change the value of the sense resistor in the driver, you can obtain the new maximum current value by using Ohm's Law. Also, additional sense resistors in parallel add current to the limit. The limit for the stock driver is I = Vsense / Rstock = 105mV / 15mΩ = 7A, this is explained above when calculating the maximum sense voltage. Now, with an R020 in parallel with the stock R015, we have to add: I = Vsense / R020 = 105mV / 20mΩ = 5.25A. All of this being said, Pacolux's Mantaray driver with both an R015 and an R020 in parallel as sense resistors will now allow up to 7A + 5.25A = 12.25A to the emitter before using their MOSFETs to throttle the output and protect the emitter from overcurrent in doing so.
All of this being said, Pacolux is overcooking its SFT40 emitter. I think 7A is plenty for this emitter. If you really need to add something using this driver, I'd use an R100 for 1.05A extra, 8.05A total. This is toast enough. Please consider that not all emitters behave exactly the same, and that one must be sure that the driver fully meets the claimed specifications, because if not final maximum current figures can be different. To illustrate this I was recently setting up a custom S21A with SST-20, using a Convoy 12-groups driver I received months ago as replacement for a recalled defective unit: presuming 60mV sense and R020 plus R050 sense resistors in parallel the unit should have attained 4.2A, but I finally got 4.7A (variations in sense resistor values also matter). Check this here, among other things related to obtaining correct measurements with these driver types when using power supplies.