Which answer do you want to hear? The one, which tells you, how the engine was intended or the one how it actually runs?
In 2015 I had a conversation with Marin about JS and JR and what would be the ideal comnination. How it should work and how the engine runs. He gave me just some hints, but it was already interessting.
The best or most efficent combos as the equal ones: 14/14 ; 15/15 ; 16/16 etc. That is how the engine was intended to work. As soon as you raise one skill, the efficency is gone. Marins said about this:
If B > A, it's again the same as A > B, you are under 100%
A = JS
B = JR
So you reach 100% only when both skills are equal, as soon as one of them goes up, you "drop" under 100%. This gave me a lot of headache, until I understood what he meant.
Let's say you are at 15/15. For the engine code this is "perfect", it is 100%. As soon as one of them go up, you are away from the 100%. You are better than 15/15, but not at 100%, this you would reach again at 16/16. My personal thought is, it calculates like that:
15/15 = 100%
16/15 = <100%, because you have now the possibility to reach 100% with 16/16. You raised the bar and there is room to improve.
16/16 = 100% again, the "perfect" spot. This 100% are better than the 15/15 100%, but they are both 100%. You get the idea?
So that is the theory, now to the real deal.
JS 20 / JR 10 is said to run better... I belive this. It is also the engines fault.
You have almost always a defender in front of you. So OD influences the shot and to compete with OD19 or OD 20 you need firepower... that is JS 20. A JS 15 guy just cannot find a good spot to shot. He cannot use his JR advantage, because he is shut down before he can benefit.
I for my part, like the players with JS=JR (I voted here for 15/15 btw). Until last season I ran an offense with a JS15/JR15 PG, a JS16/JR15 SG and a SF with JS16/JR16 skillset. Two seasons ago I was in the finals to promote to Div.1. And you know what? They were more or less shut down by OD19/20 guys. In game 2 the JS16/JR16 guy scored more than 30 points, because his opponent had OD around 15 or 16. The manager adjusted, set his best defender on him and my SF was done and I lost. After that I decided to sell my team and go down, because they were capped and I couldn't go for 17/17 on them. I just hadn't the firepower to overcome the OD players of my opponents.
And my opinion on the "JR has no influence on mid range jumpers". It has, but I think it is low. It maybe starts at the paint with a very low influence and the further you go away from the paint, it increases. At the perimeter it reaches than 100% of influence. But this is just my opinion...