wembley park approach

as far as i am aware since a "direct link" from the fast southbound platform was added, two southbound trains (one local, one fast) cannot approach the platforms at full speed, one of them has to slow down. Where exactly is this direct link and what was the system before this? In the previous set up where did the fasts connect with the local south of wembley and what was the need for the change?

It is sometimes very annoying that a fast train slows to almost a complete stop at wembley going southbound on many occasions when it is not due to stop there (Morning peak)