Printing Booklet is not symmetrical in paging

So I am trying to print a book with Booklet Print handling and it doesn't seem right because in the end it would have some extra emty space. So I tried to create a PDF with numbering to understand how it works

I have a 1-page document which Page 1 (C as in cover) and Page 16 are the Covers of the book

So Adobe should normally recognize and print pairs (1-16, 2-15,....) 8 sheets for 16 pages even distributed. This book I have correctly printed

1(C)     2     3      4      5     6    7    8

16       15   14     13   12   11   10   9

But then with my other 30-page document (Page 1 and 30 are cover pages) , I don't understand why they don't pair the same anymore? For the first two pages 1 and 2, it pairs with nothing (I placed the X for illustration). and it start with 3-30, 4-29.

1(C)    2     3     4   5    6     7    8    9  10   11  12  13  14  15  16

X        X    30   29  28  27  26   25  24  23 22   21  20 19  18  17

Why is that and I tried to finger out and even create a pdf with big numbering each page to test out before wasting the real paper.

You can find attached documents for reference.

I am really sorry but this one my best to explain the situation.