I have the same siemens level 2 charger, I've taken it down to 50% (reasonable charge time at 15/16 amps), 25%(7.5 amps) and MIN(very very slow at 6 amps) it does have an impact when I tested it at least.
There would seem to be no reason that charging speed should affect how full the battery gets charged. I realize that faster charging will cause a higher battery temperature, but the car can slow the charging rate on its own if needed. I guess in theory if the battery is warmer the car could end charging early, but I never hear of people saying that charging ends at 90% SOC or whatever, it seems unless something interrupts charging it always charges to either 100% or occasionally to 99%.
Someone theorized that a cooler battery can hold more electricity than a warmer battery, but I don't know if that is a fact or just speculation. Even if true I wouldn't think the difference would be all that noticeable, and again it seems it would be obvious from looking at the SOC after a full charge.
So it would seem to me that any changes in driving range are unconnected to charging speed. If someone experiences differently then I sure wish someone could come up with an explanation for it.
Now to be clear I am talking about actual EV range, which can only be measured using the odometer to see how far you can go on a full charge. As for the displayed EV range which is just an estimate, all bets are off on that one. The guess-o-meter can be all over the place and quite often does not match reality. If there is a theory that charging speed affects the guess-o-meter prediction, I would not consider that to be impossible. But since that would only affect the prediction not the actual EV range, then it would just be a curiosity not an actual problem.