Is stopping the vehicle in this place, in order to give the right of way to other drivers, proper in this situation?

Why?

The line made up of rectangles marks where to stop for the pedestrian crossing. It is not the stop line associated with the B-20 STOP sign. The stop required by that sign must be made before the priority road, at a position where you can check that it is safe to enter.

§ 21 ust. 2 oraz § 89 ust. 1 i ust. 3 pkt 2 rozporządzenia w sprawie znaków i sygnałów drogowych