reftex-abbrev-parameters

reftex-abbrev-parameters is a variable defined in `reftex-vars.el'.
Its value is

(4 2 "^aeiou" "aeiou")

Documentation:
Parameters for abbreviation of words.
This variable is a list of the following items.

MIN-CHARS Minimum number of characters remaining after abbreviation.
MIN-KILL Minimum number of characters to remove when abbreviating words.
BEFORE Character class before abbrev point in word.
AFTER Character class after abbrev point in word.

You can customize this variable.