Ohhh.... yes, now that I have found the picture of my sprocket, I remember from installing it that those set screws were tiny little nubbins. I don't have access to a hardware store here, so I guess I will see if I have a screw in my collection that fits, that is longer.
As for the second part, after reading your translation about nine times I finally understood, I think :-). The concern is about the body of the sprocket, above the keyway, where it is tapped for the set screw: the sideways pressure on a longer screw going into the flat part of the D could damage that end of that tapped section.
Yes I think that is definitely something that could happen. Not sure what I could do about it, other than get a spare sprocket.
What am I going to do if I don't have a longer screw? I can put the motor shaft in a vise and try to make a couple of dimples for the screws on the curved part of the shaft. But I imagine the shaft is made out of some super hard metal, and it's not like I have a drill press.
