ola.
I have done the following on all my kayaks now and in the past. Take a square piece of foam and if you have some thin hard plastic it will also help.
Step 1 figure out how high you want your back band.
now see where the the prussik cord sit on the back band. On your piece of foam mark where the 2 cords run. The piece of foam should be long enough that it sits flush un the bottom of your seat spine just before the rear foam pillar. Cut slots into the foam for the prussik cord. Now you need to shove the foam underneath the prussik cord so that your two ropes fit into the slots you cut. Glue the foam against the plastic og the back band. Once that has properly dried then glue the bottom of the foam to the seat spine infrotn of your rear foam pillar.
I find that when going for aerial moves that I often slip up the back band and that when landing say a loop you end up sitting almost ontop of the back band (had same problem with WS and Riot). If you cut the top slot deepr than the bottom it will help keep the back band at a slightly forward incline (this will also force you to keep an agressive body position).
If you did fin some plastic, glue that onto you piece of foam so that when you put the foam in place then you have the plastic on the foam against the plastic of the back band. This will help to keep your little foam pillar stif and straight.
If you do not feel the need for all of the above mission what you can also do is make sure that your bungee cords on the back band are set correctly. so the bottom bungee should be pulled tighter than the top bungee, this will once3 again get your back band into a more aggresive position.
here is a pic of back band pillar.
hope this helps
if my explenation was a mess let me know then I can send you a step by step pic and how to thingy.
cheers
d