How old are the plants and how long have you had them on 12/12?
Seed companies create these plants with specific crosses which form an F1 seed, taking two F1 seeds and crossing will create an F2 seed IBL (inbreed line) which will have a larger phenotype variation and will lose some of the hybrid vigor. It's going to be a crap shoot with what you get from your planned cross, if you really like the plant then you should clone it (which I'm not sure you can do with autos) or buy more seeds from the same company.