Yes, any timing adjustment you make will effect the setting at both idle and full advance. It's more important that you don't go too advanced. The advance unit is designed to move an exact amount and advance the timing an exact amount (25°). That works fine when everything is new but as wear sets in and the advance unit begins to loosen up, the amount it advances can grow. Yamaha compensated for this to a certain extent by giving the idle timing spec as a range, not a single exact number. It is 13° to 17° BTDC. You may have read the timing specs are 15° BTDC for idle and 40° BTDC for full advance. That works just fine if your advance unit is perfect and only moves exactly 25°. If not, then you can (and must, really) cheat the idle timing a bit more retarded to keep the full advance from going too far.
As you're set now, on the "T" mark, your timing is retarded not advanced. Advanced is when you fire too early, before you reach the "F" mark.
As you're set now, on the "T" mark, your timing is retarded not advanced. Advanced is when you fire too early, before you reach the "F" mark.