It's a good idea for exactly the reason you mentioned. But usually it is difficult to reach 1:2 with this method because this requires that the lens already achieves 1:4 without converter. You say, your 100mm lens focuses to one meter? That should yield a magnification of about 1:8. With a 2x converter you would get a maximum magnification of 1:4. Are you using some additional accessories like diopters or extension tubes or how do you get 1:2?