It’s not so much that you MUST start with the Master, but that it’s probably a better starting point than someone else’s customized curve.
Thanks for the details about your Na2/Pd mix. I’m aware that this ratio, 1 drop (or more) of 5% Na2 per ml is what B&S seems to be recommending these days, but I think it’s significantly higher than necessary. (Actually I just looked at their website and they are recommending 4-5 drops for an 8x10, which is just plain nuts, but I know why they need that much. They use standard industrial fluorescent lighting in their darkroom, which gives off a significant amount of UV, which causes the UV sensitive coating to fog. The high level of Na2 is to suppress the fog.) I use 1 drop of 1.25% Na2 per 1ml of Pd. It is enough to ensure there is no chemical fog, but does not shorten the tonal scale of the process. If you think of it in terms of graded silver paper, it’s like B&S is using grade 6, you are using grade 3, and I’m using grade 1. We can make negatives to fit any of these, but by using a higher contrast mix you are sacrificing some of the subtle highlight rendering characteristics of the process. Since you’ve already mixed it, I suppose you’ll want to stay with it, at least for now.
The graph below shows the range of exposure scale (contrast) achievable on COT320 using Pd with Na2 ranging from 1.25% to 2 drops of 20% to a 2ml mix for an 8x10 print. This is very useful for printing large format film negatives directly since is is nearly impossible to make every negative with the perfect density range. Most of my 8x10 negs print best with the “grade” 1, 2, or 3 mix. With digital negatives, this shouldn’t be a variable since we can tailor our negs for a particular density range. Your current mix gives an exposure scale of about 1.6 as analyzed in this graph. Mine is about 1.85 which is almost a full stop more range or longer scale. In practical terms this means that you need about a stop (0.3 density) less range in your negatives than I do. (I hope this isn’t completely Greek to you! Sorry if it is.)
Since you are using a stronger level of restrainer than what any of the Pt/Pd curves or the Master were intended for, it is very likely you will need to make a custom limited Master. That is probably why your first linearization is still so light in the highlight region. To do this you will need to make a negative of the LIMITER target and then print it. This process is described in good detail in the manual. But ask here if you need help.
For Tween, try one drop per ml of total FO+Pd, or 2 drops for your 50 drops which is probably a little more than 2 ml.
I’ve been in Taos for a little over 13 years. Please give me a call next time you’re here. What’s your mom’s name?