the shoulder seam sits 9cm past the joint. any further and an oversized tee starts looking borrowed.
measured from the shoulder point, not from the collar. at 9cm the sleeve breaks where the arm actually moves, and the body still reads as a block rather than a bag. push it to six or seven and the shoulder collapses down the bicep.
that is one decision, and it is the decision the whole garment is built around. the weight, the collar and the length all follow from it.