In this situation, are you obliged to stop just before the pedestrian crossing?

Why?

The visible B-20 STOP sign requires you to stop before entering the priority road, but not necessarily immediately before the pedestrian crossing. Stop before the stop line or, if there is none, where you can see traffic on the priority road without blocking the crossing. You must give way to pedestrians who are on or entering the crossing.

znak B-20, § 21 ust. 1 i 2 rozporządzenia w sprawie znaków i sygnałów drogowych; art. 26 ust. 1 Prawa o ruchu drogowym