Strange thing with ProjectWorldLocationToScreen()

I don’t understand what is ProjectWorldLocationToScreen() result in case of window game mode.
I just called ProjectWorldLocationToScreen() and located widget in this place, and I got different results with full screen and window modes. With full screen widget stay on the actor, as it should be, but in in window mode it stay in strange position. In depends on window size.

There are simply code:

FVector2D MyTranslation;
MyPlayerController->ProjectWorldLocationToScreen(MyActor->GetActorLocation(), MyTranslation);
MyWidget->SetRenderTranslation(MyTranslation);

Are there any opportunity to got equal result with full screen and window mode?