I have seen someone choose to learn standing up rather than sitting because he was tired. He felt he could stay awake better in a standing position.
When it comes to Grace after Meals, the SO O.Ch. 183 (9) rules that it should be done sitting “in order to have more concentration”. The Rema says that one will have fulfilled the mitzva even if he was not sitting.
My question is therefore if someone thinks that he can have more concentration in Grace after Meals if he recites it standing should he rather stand than sit?