Re: "Crack" noise on either forward or backcast
No question in my mind that the backcast is more important than the forward cast. I weight it 65 and the forward cast 35. By learning to watch the backcast I have no doubt that your timing has smoothed and you now adjust to subtle things on the backcast that you were not formerly aware of -- the effect of a gusty breeze being but one. The forward cast, on the of the other hand, we all watch. The trouble is when we finally see the forward cast, it's too late to correct mistakes.
In truth, many of my final casts are made backhanded from the backcast; some of my longest, too. It's a useful technique that I would suggest you practice. It make changing direction a snap!
The three principal problems I encounter in teaching the cast are: (1) Watching the backcast, (2) Keeping the rod tip low to avoid slack, and (3) maintaining direct contact with the fly. (The exception being high stick nymphing.)
As for whether or not the two parts of the cast should be mirror images of each other, I can only say that mine are not! In fact, my back and forward casts usually follow different tracks. I attribute the mirror image business to the influence of the Ancient Fish Gods on the Knot Tiers, the same folks who would lead people to believe that to be a fly fisher, you must master the 1,651 knots they write books about.
Of course, you can make the cast that way folks; in fact, the cast can be made any one of a number of ways. Years ago there was a article that discussed fly casting in ovals -- sure enough, the technique works.