Blanket statements about tensioning should be taken lightly. I've backed off my B-17CS 15 turns in addition to immersing the damn thing in neatsfoot oil for a half hour. And that was after ~3,000 miles of perseverance/frustration. It is not sagging. I am 6' & 170lbs and have relegated the Brooks to my commuter. You and I seem to be alike in that an upright riding position is the only solution unless some perineal relief is employed...such as...
Another option would be to send it to Selle Anatomica for their
Brooks upgrade. They cut it out so it's similar to the Brooks Imperial.