master HBP/PE 6 but not HBP/PE3?

In F1, I am at the 5th progression in every skill, beside the HBP! I can almost do 5x15 push-ups, but planche push-ups seem totally impossible for me! But I can easily do HBP/PE4 and PE5 and nearly master HBP/PE6! Why is that? 
And I also think that SL/PE1 and PE2 is really hard, but SL/PE4+PE5+PE6 are super easy. I don't really understand as this should be a progression and therefore harder! What is wrong with me?!^^

 

The HBP progression is not linear. You are building up pushing movements across different planes, it will eventually all come into a single multi plane pressing skill known as the hollow back press Basically you have to be able to press in all directions before you do the real thing.  HBP/PE6 is also just the tip of the iceberg when it comes to dips so don't get too excited about it. 

 

SL/SE1 is difficult for most people, it's a very common weakness. You are only as strong as your weakest link, so master it now and enjoy the rewards later on. Coach has previously said that you must first learn to crawl before you walk or run. Keep this in mind when you train next time.