If the timber is 8" wide, the joinery is typically 2" off the reference face with 1.5 or 2" mortice. So one side only has 2" of decent full peg on one side the other side, the off side, will see at least another equal 2" of good meat. Plenty in my book. The extra 4" on the far side will yield some peg length allow the flex in the peg that is desirable and of which you speak of, Jay. So all that and no damage to the relish on the tenon.