@Rodrigo thanks for your reply.
In no way I'm posting so you can fiddle with my css, I'm only hoping that something might be extremely more obvious to others than me.
You' re right about the css, It looks like the height 100% that I used in the absolute positioned pin element caused the extra height. I changed that to bottom: 0 and it worked as expected.
ysk's post in ScrollTrigger Pin Spacer creates additional height at the bottom was marked as the answer