+1, a crude test : heel of your foot on the pedal axis , leg straight ,

then once your foot has the ball of your foot over that same pedal axis

you have a slight bend in the knee as You turn the pedal past Bottom Dead Center (BDC)

Once you are used to the proper height , if the seat post slips down ,you can feel the difference.


Add: The desire to have your saddle Tilting down May indicate you set your Bars too low and Your spine,

Lower lumbar, is not limber enough to turn your Hips up and bend above yout hips ..

sloping down saddles put more pressure on your hands which have to push your butt back up slope all the time.