cipher - A Magical Cryptography Puzzle

The following is the first and second sentences of one of my favorite (and fairly popular) fantasy books encoded in a cipher I created a few years ago. I'm quite certain it's breakable, but hints/more sample text may be needed to solve it. Partial solutions are welcome. Good luck!

jrimmataFFynwqephsepUKhyjfcdozAZkgtwaemiPAckhvsbgmdkrxjaiwFAhorvycnntfAKsrafwwopxdPUmeokhieuKFpstuyxjzmdCAAAidfeidkpdwMAzzopxamckjihnpZZpfdhdfFAgwkycztyGAydhvxlsiZAdntsjwwioeFKdgixAApzbathfeedUFdithrrepoxclibswllPPyxcbkktdFZhlzpadusjaictusfUAodowAPynmgefccKUhorqtkdcZZedwvyuyyUPryyfcieaAAssofshexZKppmjfzejAUzgcsorhmAUbrehdrdajmncFUikkersxgicbbKAjxcvokAAwyzphnUUvfjkraaaaoiitpPPerzlAUtxwbezAAaailmxIAwhufdlspxxZV

Bonus if you can determine the book's title from its first couple sentences.

Hint 1: (and this is a big one!)

This cipher uses two 5x5 Polybius grids of my own creation. See here for a sample grid. One of them is used somewhat rarely in this text, but it is QUITE obvious when.

Hint 2:

As hinted at before, one Polybius grid is used for encrypting letters, and another is used for spaces and punctuation. The second grid results in UPPERCASE letters, while the first results in the more common lowercase letters. The main challenge that remains is to determine how the coordinates of the grids work.

Hint 3:

You may notice that different letters are represented by different combinations of symbols throughout the text - which is correct. However, the available letter combinations do not change. What I mean by this is that my options for giving the grid coordinates of an "E" (for example) are the same throughout the puzzle and do not change over time.

Hint 4:

In a letter (for example, "E") the second coordinate is always one of the following letters: afkpuz. What is the relationship between these letters? Check yourself by looking at the letters that can be found in the first coordinate of that letter: ejoty

Answer

I'm gonna take a random guess (well, not technically random), based on the number of words, and letters per word, that your favorite book is

The Chronicles of Narnia: The Lion The Witch And The Wardrobe

I'll try to decipher the encryption when I'll have time

Update:

Polybius grid 1:

. 1 2 3 4 5
1 a/z f k p u
2 b g l q v
3 c h m r w
4 d i n s x
5 e j o t y

Polybius grid 2:

. 1 2 3 4 5
1 space .

2 .
3 ,
4 -
5

By getting the row number and column number of the to-be-encrypted letter, we select a random letter within that row.

Example:
(1) Let's encrypt letter 'E', the row number is 5 and the column number is 1.
We then randomly(?) pick a letter in row 5, and pair it with a random(?) letter in row 1, thus getting the 'ep' pair as hinted.
(2) If you encrypt 'space', 'A', or 'Z', you choose both letter-pair from the first row, that's why most of the capital letters (space) can be found from the first row (A, F, K, P, U, Z).

I'm not sure if this is the right solution, but the process checks out. But if it is correct, we can't actually solve the problem/future problems unless we know the original message because of the random picking of letters.

My bad, it is solvable, was confused.

So, in the first pair, 'jr', we can see that 'j' is in row 5, and 'r' is in row 3. We can then get the original letter as 'o' because of it's coordinates, (row 5, column 3).
Second pair is 'im', getting row 4, column 3 = letter 'n'.
Doing it to all pairs, we get the first two lines of The lion, the witch and the wardrobe:

Once there were four children whose names were Peter, Susan, Edmund and Lucy.
This story is about something that happened to them when they were sent away from London during the war because of the air-raids.