  The spectrum and variability of the Seyfert galaxy MCG-6-30-15 can be
decomposed into two apparently disconnected components: a highly variable power
law and an almost constant component which contains a broad and strong iron
line. We explore a possible explanation of the puzzling lack of variability of
the iron line, by assuming that the variations of the power law component are
due to changes in the height of the primary source in the near vicinity of a
rotating black hole. Due to the bending of light in the strong field of the
central black hole, the apparent brightness of the power-law component can vary
by about a factor 4 according to its position, while the total iron line flux
variability is less than 20 percent. This behaviour is obtained if the primary
source is located within 3-4 gravitational radii ($r_{\rm g}$) from the
rotation axis with a variable height of between $\sim$ 3 and 8 $r_{\rm g}$.
These results revive the possibility that future X-ray observations of
MCG-6-30-15 can map out the strong gravity regime of accreting black holes.
