simulate.volumeCorrection Issue

[caganze]

coord=astropy.coordinates.SkyCoord(ra=189.07454167*u.deg, dec=62.24205556*u.deg)
import splat.simulate as spsim
spsim.volumeCorrection(coord, 0.0, 1000.0) returns 1.0
spsim.volumeCorrection(coord, 1.0, 1000.0) returns 0.17

Shouldn't these numbers be close because there is no difference between 0 and 1000 pc and 1 and 1000 pc in the same field of view? I have not been able to track the exact issue, everything seems correct computationally.