Tetgen Mesh Coarsening

Hi,
I want to do mesh coarsening using Tetgen and I have tried a couple of ways but none of them has worked out yet. All i get is a very absurd mesh, where the actual geometry is completely lost.
I have tried giving .pointmtrlist (passing large numbers) and then using "-rR" or "-mR".
I also tried "-a0.9R", but I suppose this is a wrong command, because i get no results.
Any help would be appreciated.
Thanks
p.g.