I focused on the effect of the LED rather than all variables. Yes, reflector proportions and dimensions are just as important as LED when it comes to spot size.
A very good writeup is here:
Long story short:
Nearly all reflectors are sections of a parabola. Sometimes longer, sometimes shorter. Or the same in other words - deeper or shallower.
Hotspot intensity is proportional to reflector area.
Reflector shape being equal, spot diameter is proportional to reflector diameter.
Deeper reflector of the same diameter has smaller hole in the middle - so it throws better, but only slightly.
It also puts more lumens to a beam (not very much typically), but makes it less defined - the spot is smaller but it comes with a larger corona.
How much estimate allowance for the spring when using a 21700? Fully compressed? What will be the cons for a fully compressed spring? Adding much more resistance and create more heat and having a chance that the spring will collapse?
I have some P42A that I have no confident or not comfortable using them on the FT03.
Current is in the mid-twenties. I believe the tiny D4 already draws 16A, so you have only seconds on turbo but people are ok with that. Mass and surface of the FT03 is way higher so it should be ok. The main worry is if Astrolux has adapted the circuitry enough well to all those amps (the D4 has great connctions inside), any weak electrical joint will break eventually.