Low contrast is a sign of under development. I developed a roll of Tri-X in undiluted D-23 last night for the recommended 7.5 minutes as part of a project. The results were quite similar to D-76 (1+1) for 9.75 minutes, but the grain was somewhat softer and the sharpness was somewhat less. Simple scaling would say that the development time in D-23 (1+1) would be about 10.5 minutes, but the massive development chart recommends 13 minutes. Even undiluted, D-23 shows some decided compensating effects. At 1+3 it is very similar to the Windisch compensating formula, which is well known for massive contractions on the order of N-4 or even N-5. Highlights and upper midtones would be greatly compressed. When diluted, D-23 exhausts quickly, and it should be used as a one-shot at dilutions greater than 1+1.