Which post are you refering to?
Subtleties–>subtitles
“And **idea => ideal **adds a letter and subtracts a syllablle.”
Syllables are not cut-and-dried… But, to me, you either pronounce both “idea” and “ideal” with two syllables, or you pronounce them both with three.
But I do see how you could analyze “ideal” as two (many would say the word “deal” has one syllable), while requiring “idea” to have three (since the “-ea” here is clearly not a single phoneme, as it is in, say, “pea.”)
Only four letters, but
tomb->comb->bomb
A mathematician and a chemist pronounce (and hyphenate) equivalent entirely differently. Although not an example of the OP, consider what happens to finite, when you prefix in-.