If you give it a little thought, its almost too obvious.
Here is some food for thought:
If you add weight to your front squat, everything from your core up to your shoulders is becoming stronger. Your body is doing work by supporting the weight on your delts and staying in a tensed upright position through the movement. Even though you are not pushing the weight with your shoulders and triceps, they are still becoming accustomed to supporting the weight.
If you get your Front squat up it would be impossible for your Overhead Press not to follow. They are practically the same movement CNS wise, in both of them you are in the same position, and you are pushing explosively. Just because you push with your legs on the squat, and with your shoulders and arms on OHP press does not make them completely independent movements. Gains on one will translate to the other, I promise.