Look at this Distributor orientation..

In a perfect world, the rotor would point directly at the plug tower at 25-30 degrees BTDC. That somewhat "centers" the rotor as the timing varies from maybe 5 to 55 degrees BTDC. I've always tried to make this work by a combo of tang position and plug wire position on cap. The spark will jump to the nearest cap contact so you don't really want tdc to be directly at your cap contact as that would put the 55 btdc too close to the #2 cap contact (the one prior to #1 firing). It will still work if you do line them up but I'm more comfortable having it somewhat centered.