The bowl can't rock, or it will break the seal.
Some bowls don't have much toward the back to prevent someone from rocking back and forth.
So........a bowl that in fairly long on the bottom, with a good portion of the bowl behind the bolts for balance,
Make sure you have compression on the wax, sometimes it takes two wax rings.
Make sure it flat to the floor or shimmed to make it so,
PolySeamSeal around the bowl, except at the back, to help "stick" it to the floor.