Getting proper DR

I have started to get serious about getting the right DR for platinum prints. Most of my attempts have been with negatives at a DR of ~1.1 -1.2, that is from taking a reading from the densest part to the lightest part of the negatives. I mostly get this with regular processing and some selenium toning of the negative. Last night I shot a still life with the intent of the negative being specifically for this process using Hp5+, metering with a incident light meter( could not find my spot). Rated at iso 400. Added 2 extra stops for bellows extension. Developed in D-76 1:1 Jobo for 18 minutes @20C. It was a still life with dark flowers and a slightly off white vase Zone III background. DR was ~1.2... Really would like to get a negative that is in the range recommended for pd/pt printing. Any suggestions? I suppose another 2 minutes or higher temp? I used the recommendations in Arentz Platinum printing (well even added 1min to dev time).

Thanks