The insight concerns the word אגדה - it is spelled חסר in the סידור. The letter missing from the sequence is a ב because the letter Beis represents duality and separation - the antithesis of our quest לאגד.
Furthermore, the gimatriya of אגדה is 13 - אחד. No further explanation necessary.
The question - to which I do not yet have an answer - is why in אתה גבור the first שם is spelled אדנ-י and not, as the rest of the names in Shemoneh Esrei are - with the שם הוי"ה. The first שם in thew Shemoneh Esrei is also a Shem Adnus - אדנ-י שפתי תפתח - but there are reasons given for that permutation. I have not seen any reasons for this permutation.
Answers are welcome!