Dudes everyone can turn the upper body and still be pure open stance (feet lined up parallel to the baseline). That is not how pros hit powerful forehands. They usually have their right foot behind the left foot before they start their swing, which gives them more space and power. That is what is called being sideways.
Even the great open stance artist Nadal has the left foot slightly behind:
See how Roddick starts off with both feet aligned parallel to baseline but the right foot is back before he hits:
The other important point is hitting through the ball. It is not about hitting across the ball, but hitting through it. And the role of racket manipulation in fixing the direction - it doesn't come by the same swing and some different contact point in a risky tangential collision with the ball. It comes by planned contact and hitting through the ball.
5263 has no answer to it that is why he is quibbling about open stance positions.
I will be going with what the pros say and do. That is why I got the clarification. Some pros may not be able to articulate well, but this guy is not like that. Hit through the ball is NOT hit across the ball. Those are real words from a real high-level player, not some vague made-up phrases from someone who has never played the pro game.