That seems like rather venue-specific advice. In the average lecture hall or conference room I've presented in, all the seats can see the full screen just fine

That seems like rather venue-specific advice. In the average lecture hall or conference room I've presented in, all the seats can see the full screen just fine. In fact, I've sometimes put important graphics as low as possible, knowing the lights in a particular room tended to wash out the top half of slides a bit.