Error in Custom Barrel GUI 1.20.5+ Guide /// Font GUI background on 1.20.6

Followed the guide in this server (https://datapackhub.gitbook.io/custom-barrel-gui-1.20.5+/advanced-gui-with-font-bg/setup) to the letter and it does align the GUI however it shifts the entire thing by the negative space?
/data merge block ~ ~-1 ~ {CustomName:'[{"text":"\\uFFF1","font":"lexiccn:automatic_brewing_stand"},{"text":"\\uFFF2"},{"text":"\\u0001","color":"white"},{"text":"Automatic Brewing Stand","font":"minecraft:default"}]'}
Testing by standing on a barrel and running this command.
I find if I remove "\uFFF2" (being the -169 advance) then the result becomes the second picture, where the GUI is aligned, but the next is not.
It appears the negative space is shfiting both everything before and after it and I'm not sure how I fix this?
This is with Vanilla 1.20.6 in a singleplayer world.