* Sen - The "e" in this part of the word is part of a vowel digraph (a combination of vowels) "en", which makes a long "e" sound, like in "see".
* Tence - This part of the word has a silent "e" at the end. This silent "e" makes the "e" in the word "ten" long.
Therefore, "sentence" does not have a short "e" sound. It has a long "e" sound.