Dual N back

[Ninjaplex]

I need help this is imortant how do you seperate the audio stimuli and also visual stimuli since they both occur in the same time its hard for me to seperate them I usually say for example L is in top right F is in bottom and I think that is chunking I still compare and update my working memory but isnt that chunking still what do you guys think am I supposed to seperate and if I do how do I do I just imagine the letter in the middle that might be bad because if a square occurs in the middle then it might look more convincing both of them are linked or do I just imagine the letter I dont know what to do please help