Q: As to your statements: "Then he was confused about your statement that he should adjust height to the distance...it didn't came instinctively to him - or, better to say, he was too worried about should his arm go straight up...or little bit forward ( I think that he's still confused about this)...and thinking too much stood in his way of learning (I guess...)...
A: Yes, to control distance you simply change the direction (angle) of your Release. It depends on how much UpForce you are generating, and how far away you are and how quickly you have to shoot. Adrenalin and fatigue are part of the equation, too. With practice and trust, you will know what angle to give it so that you can go "full out" every time, without holding back, and simply adjust the height. Your arm will not go straight up unless you're under the basket. It has to go up and forward, whatever's appropriate.
Think of your right arm (I'll assume you're right handed) as the hand on a clock. Think of the center of your chest as the center of a clock. And think of it as someone is looking at you from in front of your body, so if your right arm is out horizontal to the right, that's 9 o'clock to your friend, and if you raise it, it becomes 10 o'clock, then 10:30, 11, etc. A flat shot would be something like ~10 o'clock, and a very high shot might be 11:15 or 11:30. 12 o'clock would be straight up, not appropriate for shots except from under the basket, as I said.
As you shoot, don't try to get a certain "time." Just know you want to go as high as possible, based on how much power you're getting from your middle and lower bodies (UpForce, "Leg Drive," "Leg Lift," whatever you want to call it). I say it's "instinctual" because you'll just "know" what angle to push your arm at from practice and experimentation. For most shots you want to "catch" all of the UpForce (100%), because it stabilizes the shot, the higher the percentage, the more the stabilization factor. You will feel an effortlessness when you connect to that power. Don't "under-jump!" Always give it at least enough to get the ball there with high arch, and if you give it too much, you can always go higher. If you're under-powered, you'll be short or have to add extra muscles, thus adding variables.
(One thought: From what your coach is saying about hitting the trees, it's possible you could be shooting "too" high. More than 6 or 8 feet above the rim gets a little hard to control, I feel. If you have that kind of strength, then raise your Set Point up higher, thus making it harder to block, and also allowing you to go more quickly and more full out, without worrying about being too strong, and that will lower the arch, too, if that's desirable. Most players' shots are too flat, and very few players shoot too high, but it could be happening. Just check it out. If you go too high, then gravity starts to accelerate the ball when coming down, and it's a little more difficult to control ball flight. Again, check it out. If you're draining everything with the height you have, then keep it that way. Note: Please observe your typical height and tell me what it is. Thanks. Also, if you can video tape your shot [in VHS format], send me a tape and I'll give you my comments. I'd love to see your shot.)
Key is the mastering of the "pure" Release motion. Always start your shooting practice from what I call the "Zero Point" in the video. I don't like that name any more. It's not a point. It's a semi-circle, and I call it the "Pure Release Distance" (PRD) now. Find that distance where, with no legs or just a small "triggering" motion of the lower body, you can do your "full out," to-the-end-of-the-arm Release motion and the ball flies high and true, dead center, every time. Your Release will be aimed upward at a high angle, and the bottom of the ball will get to 11 1/2 or 12 feet above the rim, then descend softly, dead center. By "full out," I mean about 70-75% of max. speed and force. It's a motion you can do comfortably all day long without strain or pain. Develop this "AUTOMATIC RELEASE," a no-brainer, no-thinking kind of motion. The speed and force do not change, only when you fire the Release and the angle you shoot at. From the PRD, the angle stays pretty much constant. If it feels awkward to have no leg action with it, then add a little horizontal rocking motion or an up-on-the-toes kind of action, if you want, to trigger the motion.
Start every practice like that, and spend a lot of time there. Don't just do it well a couple of times and then think you "have it!" When it's getting more and move consistent and repeatable, then move back slowly and incorporate the UpForce.