Two thoughts here:
- Don't frame so tightly. That will help to allow for parallax. Of course, that goes against our instinct, especially if you've been shooting with SLRs. I have this same issue with a Super Ikonta 6x9, and I have to remember to correct for vertical parallax when shooting anything closer than about 10 feet or so.
- Try an external viewfinder. Zeiss Ikon made a turret finder for the Contax IIa. It's a bit costly, however, it does allow you to correct for vertical parallax, and the way it's constructed, it centers the eyepiece over the lens, which means that it automatically corrects for horizontal parallax. The downside is that this viewfinder is a bit costly. It generally sells for about $225, but sometimes you can chance upon a good deal and get it for less. The Soviets made a version that is identical to the prewar turret finder made by Zeiss Ikon. The location of the accessory shoe for the Kiev / Contax II and the postwar Contax IIa is different, and that's why it's best if you use the correct finder for the camera that you'll be using.