This is informative -- it looks to me like the density of polygons goes
up dramatically near the center, and I suspect this is why oconv is
unable to resolve your model. Oconv has an upper limit to the number
of polygons it will put in an octree voxel, and you are running into
this limit with lower values of -r and running out of memory as it
tries to resolve the mesh with larger values of -r. The best solution
would be to reduce the number of polygons you have in the center of
your reflector, perhaps by going to a more sophisticated grid
arrangement that what you have, which appears to be a uniform division
of the polar coordinates.
You might also try a recursive subdivion scheme using spherical
triangles. A dodecahedron is a good starting point. This would solve
your problem, although the number of triangles can explode with the
subdivision level. Of course you'll have to implement this yourself, but
it's actually simpler than it sounds.
END OF LINE. (MCP)