Because of Sheik's poor kill power and that her best kill setup is dtilt/ftilt > uair they will want shorter ceilings. While Ryu also kills off the top and in theory should want shorter ceilings as well, however banning shorter ceilings is a much larger disadvantage to Sheik. If you can force it try to go to BF. Their kill window shrinks substantially, while Ryu still kills consistently.
Ryu