I had the same problem with Kentona and arrived at the answer purely by chance. I started mixing my PF 130 with distilled water solely due to the 130's long life. I wanted to reduce the chance of contamination as much as I could. Voila`! Kentona suddenly looked better. Also found that two to three minutes developing is needed.
As much as I liked Kentona, there needs to be a grade 3 version of it. I never have had much success in getting contrast to increase very much.