1. Centre of saddle height from bottom bracket.
2. Nose of saddle setback behind bottom bracket. The most accurate way of doing this is to place the back wheel against a wall and measure the distance horizontally (1) from wall to bottom bracket (2) from wall to tip of saddle. Divide and replicate on second bike.
Both the height and setback are now the same - seat tube angles don't matter.
3. The only variable left is stem height and reach from saddle.