Hi @VarianceCivet85
Welcome in the Community !
When creating your Space Filling design to generate your candidate set, you can very simply achieve your goal by using Disallowed Combinations Filter or Disallowed Combinations Script.
Select "Use Disallowed Combinations Filter", and select factor Dtype = P and the range for factor D from 10 to 20, OR factor Dtype = A and the range for D from 10 to 20. These are the factors ranges/combination you don't want in your design based on your informations, you should have this screen :

If you are more familiar with JMP script, you can use the option "Use Disallowed Combinations Script" and this script:
Dtype == "P" & D >= 10 | Dtype == "A" & D >= 10
And you'll get the same results.
Specify the number of points you want for your candidate set, generate the datatable, and you can finally check that the constraints are well enforced and respected:

I would recommend reading the excellent blog Demystifying Factor Constraints by @Jed_Campbell, it will explain the different ways to enforce constraints when creating designs/candidate sets.
EDIT: As you want to create starting points for Bayesian Optimization, you could maybe use a D-Optimal Custom Design and enforce the constraint mentioned before, to be sure that the range for each factor can be explored with a minimum of runs. With only 6 runs and Fast Flexible Filling design, I had some situations where the ranges of D for every Dtype was not fully explored :

With a Custom design approach (and only using main effects in the model), you'll need a minimum of 7 runs, but the repartition of the runs ensure you will explore the entire range for any Dtype level :

Hope this answer will solve your problem,
Victor GUILLER
"It is not unusual for a well-designed experiment to analyze itself" (Box, Hunter and Hunter)