I'm not sure if this is a trick question but I'll answer anyway.
Under Derek we played a man marking system. It was very rigid. At times we had a forward running from full back to full back chasing the ball whilst everyone else moved around following one player. From what I've seen of Glass it's a fluid system where we press as a team. It's not about plan a, plan b etc it's about adapting and reacting to how the opposition move the ball so we can force them in to a mistake and counter.
Things absolutely changed under Glass, but results were still indifferent. He took over another mans team that looked to be lacking in confidence and fitness and the different to see after several months is clear. Rangers away you could argue we were the better team. We missed two of the biggest sitters you are going to see against a team that steamrolled almost everything put in front of them domestically.