Sewing a fly front zipper

[Futura]

(I learned the hard way today not to try and work while unwell... I somehow cut a hole right into the fly lining and had to rip everything out. Hopefully tomorrow I'll finally get antibiotics and be on the mend. Thank goodness the rest of the material is otherwise intact.)

Do women's trousers ever have a fly lining extension piece sewn onto the front fork? I've not seen a women's fly front ever constructed in this manner. Their fly front instructions start on page 26 (printed).
https://drive.google.com/file/d/0B8mTVOscTHS1ZVJ1Rk9WNjBuY3c/view

Would the lining "tail" help the fly shield lay flat? All of my ready-to-wear jeans are cut with the shield as an awful folded lump of denim (as expected). Every single pair ends up with the shield folding back on itself, resulting in 6+ layers of fabric in one spot. Not comfortable and not pleasant to look at in the least. There's also no way my machine will handle sewing through that much!

Any suggestions on how to cut such a lining? The fly facings I'm working with at the moment are 2" wide, and the zipper curves down just a little bit into the crotch curve in order to fit over the hips. The book above merely states to "[c]ut a piece of lining on the bias the shape of the fly facings but slightly larger and with the extension as shown (Fig. 26-4)." I'm unsure of how to cut the extension.

I'm also confused on how the lining covers the seam allowance in Fig. 27-2 (page 28). Does the folded edge of the fly lining merely lay directly over the seam allowance, rather than wrapping around and enclosing them? I imagine it would just lay over the seam allowance, considering the basting shown in Fig. 26-3. Does that sound correct?

Poulin's "Tailoring Suits the Professional Way" says on page 141 to "[c]ut a flap lining out of heavy pocketing material in the shape of the right fly piece, but 1 1/4 in. wider and with a 'tail' at the base 1 1/4 in. wide by 3 in. long." (https://archive.org/details/pdfy-6x5RRDlrC8nRAeWc/page/n139)

I suspect this might be easier for me to comprehend when I'm feeling well again!

[mysewingpleasure]

Futura,
I learned the zipper construction by this video, recommended by Peterle, regarding the tail of the facing.

http://movsd.com/BespokeCutter/index.php?topic=422.0

I can never imagine how neat a zipper construction can be until I saw Sebastian's demonstration. And it is the best video in the world. I wish I can understand all what he explained.  I used to make ladies pants, I do not make the extra tail for the fork. It seems to be that is only for men's trousers.

[Futura]

Thanks for sharing the link to those excellent videos!  I'd seen them a while ago but forgot..

I'd always thought that only men's trousers would have the lining "tail" sewn onto the fork. I wonder why that one book has women's pants sewn the same way.

Is it possible to cut the lining extension in a manner that it would fold down this evenly? Or am I driving myself mad trying to achieve the impossible?

[JM MacLachlan]

I think the Poulin method is solid in its making. It's very close to how I learned years ago. I hardly make zip flys, as most of our clientele orders button flys. However, It was a hand reference when I do get them.

[mysewingpleasure]

As JM suggested ,  I find  this link below,  at Page 72, the method is for button zip fly, the facing shape is cut in differenct shape and the tail is one inch wide and 3 inches long.

http://www.cutterandtailor.com/forum/index.php?s=31467c4893cb0c31f43bdad414d3bbf2&showtopic=2968&page=2

As in Sebastian's video, i guess his facing is about 2 inches wide, as in 14:05, after he attached the facing to the body, he folded it in a angle, as in 17:21 - 17:42, it ends up a lot narrower, just enough to wrap the seam allowance around and stay stitch. It is very neat.