Hi @Teenz,
A warm welcome to the Bunnings Workshop community and thank you for your question.
The best way I can see to do this is to use the longer 2700 x 600 Prempanel Acoustic Panels and put the join at the top. This is because at a height of 2700mm, the join will be further from sight than it would be if it is located at the bottom of the panel. Being further away, means it will be less easy to spot.
You can attach the full size 2700 x 600 panel to the wall following the installation instructions, then use the guidance to cut the 300mm pieces for the top, ensuring the battens are cut perfectly square.
You should then use the same method to attach the 300mm pieces to the wall and use wood glue on the top of the 2700mm battens and the bottom of the 300mm battens to glue them together perfectly in line.
Once everything is dry, remove any glue that has squeezed out of the join and assess the quality of the join. If it is more obvious than you'd like, you can use timber filler in a colour to match to help conceal the join.
Let me know what you think and if you have further questions, please don't hesitate to ask.
Jacob
