The sharp drop in the flux striking the accretion disk
  In this paper,We present a simple relativistic approach to analyze the flux striking the disk which is possibly from a source up the Black hole.The X-ray source is locate above an accretion disc orbiting around the black hole,this assumption is invoked by recent studies about iron k$\alpha$. we compute and arguing that due to the light bending effect near black hole, the flux striking the disk surface may be very concentrated,which will undoubtable change the disk's ionization state hence change the iron line's ionization state and emissivity.Also,Our model may explain the steep power law when modelling the lines. 
Huang Wei