I believe a 'tri' setup is moving the saddle forward to ease the hamstrings.
Moving the saddle forwards opens up the torso-thigh angles so you can achieve an aerodynamically good position without compressing the abdomen and limiting the movement of the diaphragm.
Moving the saddle forwards opens up the torso-thigh angles so you can achieve an aerodynamically good position without compressing the abdomen and limiting the movement of the diaphragm.