Engineering your own voynich

[Scarecrow]

Could it be that there are different encryption rules for words in mixed case and others for all lower case, maybe even for camel case (uppercase in middle)?

Like (and not assuming anything here is correct, just as an example):

Ciphertext Plaintext Rules Applied
FaiT       WHAT      Mixed-case
Tiiiig     THREE!    Mixed-case
nmaei      HELLO     All-lowercase
fieeean    HOWEVER   All-lowercase
Kimb       HALT      Mixed-case

Cipher  Plaintext
letter  letter      

t        O 
e        T/E/V/W    Position-dependent
a        H/E        Context-dependent
i        O/R        Context-dependent

Example Encryption Process


Split input into words and  for every word, If contains uppercase letters use mixed-case rules else use all-lowercase rules. Some exceptions.
Then Combine results

Example Encrypt "WHAT" -> Mixed-case rules: F (W) + a (H) + i (A) + T (T) → "FaiT"

Encrypt "THE": All-lowercase exception → "qar"