Agree with CD, gitto, it's too scientific an approach, best advice was from Loge, to highlight the 24 letters and things should become clearer quickly.
If it helps, the 24 letters run in 5 straight-line blocks from or through the rectangular zone.
To sum up, this was like completing a jigsaw with more than its first share of blue sky, no edge pieces and blindfold! As others have commented, not worth the effort in terms of the thematic material..... But each to their own I guess.