In this case, don't fight the style, fight the opponent. Make it more personal using tactics, exploiting his individual combat behavior - reactions and preferences as well as his particular physical skills. While the opponent's system has strategic implications, it's the individual that provides the tactical opportunities that will be the major factor.
I'm going to go out on a limb and say that you can't separate the individual from the style. It's the style that opens the opportunities and provides the defense. The individual is just vehicle that the style travels. In other words. A BJJ practitioner is going to do BJJ, It's not like some traditional martial arts where someone trains System A but doesn't Spar using System A.
Style = Engine of Car
Body of car = Individual
I don't know how you can separate the two. The only person that can separate the system from the individual, is the individual.
When System A spars System A then. System A only knows the Offensive and Defensive strategies of System A. When System A meets System B (who has the same problem). Then the person who is able to quickly learn the offense and defense of the other will have the advantage.
However. Had the individual of System A sparred against System B in training Then System A will be at an advantage from the beginning. System A would now be informed about how to attack and defend against System B.
Real Story Very Simple
My first time sparring against the Sanda School in Atlanta went like this.
Initial thought.
Me (student)
1. I understood Sanda enough to know what they would try ahead of time
The 2 Jow Ga Instructors
1. They were just going to go in and spar like they do in the school System A vs System A
Training.
Me
2. Trained low stance to use against grappling attempts. I knew they wanted some take downs. (Use what you train. Right?) I change my approach and training of Jow Ga to fix this format "System A vs System B"
The 2 Jow Ga Instructors
2 They said they will use the defenses that were taught in the school "which are functional " but they are functional for high take down attempts. When we train the techniques, it was System A doing the technique on System A. Ideally it would have been better to get someone who does single leg take downs frequently to feed us quality take downs.
The instructors had the mentality of "System A vs System A"
Day of the sparring match
3. I used the solid rooting of Jow Ga to defend against someone trying to lift me and was able to successfully defend against take downs.
3. They approached as if Sanda students were going to spar like Jow Ga students and ended up getting tossed.
They knew Jow Ga techniques and concepts but abandoned them (They separated themselves from the system).
I knew Jow Ga techniques and concepts and embraced it. (I remained the Jow Ga practitioner and not the guy who abandons training)
The Sanda students fought 3 systems that day. Jow Ga Kung Fu, Brawling , and Boxing . Out of those 3 systems. Which one do must of use have experience going against? That sanda school would have easily had many sparring sessions against 2 of those systems. As a result, they were already informed on how to apply Sanda to those systems.
The 2 instructors didn't have an informed approach. It was their first time against Sanda. They didn't even bother to watch the videos of the Sanda students sparring competitions. I must have spent 5 hours watching their videos and trying to understand Jow Ga in the context of using it against them. As individuals, I didn't know them. But I understood the system that they were going to try to use against me.