removed plaster arch what level to set plasterboard at?

Hi folks.

I've removed a timber/plasterboard arch from a room to make it a square opening (it already had a lintel etc). To make good the top corners of the opening I plan to set plasterboard up against the exposed brickwork with dob and dab or battons to form a neat square opening for a plasterer to finish off for me.

Question: do I bring the new plasterboard up to the same depth level as the finished existing plaster on the pillar that is sound, or do I set it slightly below so he can render and skim on top? (the existing pillar plaster is brick + 20mm render + thin skim. (e.g no Plasterboard)

or am i better to just set it level and he would skim only on entire pillar?

most of the plaster below the alterations pictured is sound, hence my question.

many thanks