The 40CU PS5 die is rumoured to be around 310-320mm^2. It is unlikely those additional 16-20 CUs would take 90-100mm^2 (assuming a fifth gddr6 controler) in the XSX. It's still a guessing game in the end.
Aquazhi from Taiwanese forum who has been leaked info and said Xbox X (Scarlet Arden) die chip is around 350 mm and Oberon PS5 chip is 300 mm is proven bogus and fake. SO the number of PS5 using 40 CU and small die chip size cannot be used as fact. Even the 36 CU figure from Github are not confirmed to be on PS5 chip and the of the test date are very very old.