Complicated Vigenère cipher - Cryptography. Match index?

Question

Encryption

Hello, there is a text of this kind:
YUEZHSHBEMPVZNTRBSHSKHPYURBZYMNLSHEUIEZHZHGYABHRTZESHENZHZUBVSHEYNAVPEPSHEPRIUOBZHDLKSHEHVYUAYASHLLYADYAGEYMYURPAYASHLESPEIUEUUIYUGSHYAZHSHCH LVZMNTSYAYDGKMZHPMESHMOYUTLEAVPYFSHHREAMGIKSCHDZIDFYOSPEKZHYUYOZHEOKYSMSHCHRPPNMEOLIOGKPBKSHZHULYLESHYUZHTPEKBMNRFYUKADYAKBRZVSCHDHYVEF CHYAHIVRYAVAYEACHIZHGRTHHKULZESHYZHKPCHYAGTSSCHYBPNGKDMUTGZFSDCHIRSHSZOFESHOCHFHEVSYROTYAEZHPTKKPTSYEOVOBDVMGEFBSCHSCHYCHGYUYAGFSHYUGYASHEBBYUP FIBIAYAYUUTDLRGEABCHEUYAESH
383 character length (without the letter E, and probably b is replaced by b), it is possible that the key may be a random sequence of letters. It is only known that the original text was first encrypted using the simple replacement method, then over the Vigenère cipher.
Starting to parse this ciphertext, using the match index, it was found that the key period is 13 characters. But the highest value falls on 26 (attached screenshots). I started trying to do it, but a problem arises that I don’t understand what to catch on when selecting the key, because when we decrypt Vigenère, we get a text encrypted by a simple replacement, and it’s not clear on what principle to pick up the key.
Has anyone come across a similar issue or have any ideas?

Answer 1

too small a base for statistical analysis.
and how a simple replacement was made known?