It is true that developing film in Dektol can lead to very high Contrast Index, for example I show CI over 1.2 in Dektol 1:2 when I once grabbed the wrong bottle. But deliberately developing in Dektol can lead to low CI. In my test I diluted 1:9 to give me a reasonable development time.
PE, a subscriber here, tipped me off that the old "rule of thumb" is to develop for as many minutes as you dilute Dektol. So following this rule of thumb dilution of 1:6 would be for 5 minutes or 1:9 to give 9 minutes developing time.
Here is more information about the test I performed: My test was 35mm Tri-X in Dektol 1:9 at 68-degrees F
4 min - CI 0.42
5 min - CI 0.50
7 min - CI 0.55
9 min - CI 0.67