One trick I did to Swift once.. I could not help it.... Big fat lot moon craters etc. Here comes kid in Swift wanting the space next to me after crossing 5 acres to get to me. I eased her into reverse and gently let the clutch out and rolled a smidgen slower than Mr Swift His tractor started rocking side to side as he began to work that wheel trying to get that trailer just so next to me. I finally ran out of room at the far end. And he backed in. I love playing these games. He he.
I still believe it's a combination of skill and luck. You can back into a spot 10 different times and never do it the same way twice. Some days, your skill will help you get lucky and nail it on the first try, and other days, you'll get a little lucky so it looks like you have mad skills...
Just keep on practicing more and more. There are perhaps some 15 foundational tips about backing, but simply knowing them is not enough. Calculation is acquired with experience/practice and cannot really be taught. Spend a couple hours backing up in your 34hr break. It will get better.
Here are some foundational tips, but before that you should know that the initial backing position is not very important. An experienced driver can back it up in all sorts of initial backing positions. What they taught you in school is the very basics. Use the center of your trailer tandem as a guide. Watch where it goes. Pretend the center of the tandem is one axle with two tires. If the parking space or dock has lines, you don’t want the tandem driving past it. Have the tandem/tires follow it nicely. Jackknifing the trailer will make the trailer pivot at the tandem to the point the trailer won’t travel anymore, but spin like a top. You want your truck/trailer a bit jackknifed on the initial backing position. This helps the trailer turn faster. The longer you keep your steer tires fully turned, the less the trailer will travel. When the truck/trailer reaches the jackknife position, it stops traveling. This means that when a truck/trailer is straight and you fully turn your steering wheel and hold it, the trailer will travel more and turn less before arriving to the jackknife position. The closer to the jackknife position, the trailer will travel less and turn more. There are many more tips out there.
Don't turn wheel too much. Less is more, and watch what your trailer is doing. Your trailer will tell you what to do
Yeah, there comes a point where you need to forget about setups and procedures. IMO, the more you think about it the worse it gets. You just need practice, enough that you don't think about what you are trying to do and just go by feel. You mention doing better at correcting and judging distance. I think that is the time to start trying harder backs. I think I learned the most from backing into the harder spots and bad setups, it made the rest much easier, you get a feel for how the trailer reacts much better, IMO. Try some harder ones and then when you need to do a 45 it will be easier. When you just turn the wheel without thinking about what you are doing then you are at the point you just need practice and time, setup and procedure only makes it harder, like a bad habit. I think you may be close. For me, pulling and doing a "half grass" setup is easier to back into than trying to plan for the perfect setup. like my subconscious knows what to do and I shouldn't fight it.
Here's how to set up the 45: Drive past the end of the dock lane as close as you can on your left. when your tandems are centered in the lane, turn your wheel hard right, keeping the same speed. After you've turned 90 degrees and are facing away from the dock, turn the wheel hard left. When you are again parallel with the dock, STOP. Straighten your steer tires, and back your tractor straight. Now begin to turn your steering wheel to the left gradually while watching your trailer tires. The key is to put your trailer tires where you want them, not the back of the trailer. Watch the tires. Hope that helped.