If I understand your question, you understand the optimal hand width for a regular bench press, and you want to know what the optimal width for close grip bench pressing is?
In short, anything more narrow than your regular grip, all the way until your right on the edge of the knurling, with no part on the smooth part of the bar. The closer the hands the less chest involved, the more you will need to tuck your elbows, and thus maximize use of the triceps.