Really interested in your work. Great that you're spreading the your own lines of heavy CBD plants.
When you make any feminised seed then there will always be a range of individual phenos. So even when you make a hybrid cross between two different high CBD parents, there's going to be high THC plants if one of the parents has high THC genes in its make up. I'm supposing you're working the plants using traditional male/female method and then testing different female individuals?
I would suggest making S1 (reversing the females with silver and pollinating themselves) generations of your chosen females first. This way you can tell what prominent genes are in each of your chosen female parent lines. If you then grow some of the female s1 generation, test their flowers and see what dominant traits (or new traits) show themselves, you'll have a better idea of what's inside each of your females. You might even find better females from the S1 generations which will be more stable for your work (this is because effectively you're using an S1 that will be inbred with itself) and are higher in CBD.
You could then use a female S1 parental from each of your female lines to make your all female hybrid generation. It's possible that this might make a much more solid hybrid that could have a higher percentage of CBD plants within the female hybrid generation.
I hope that all makes sense.. Would love to see some pictures of your plants