reftex-allow-detached-macro-args

reftex-allow-detached-macro-args is a variable defined in `reftex-vars.el'.
Its value is

nil

Documentation:
Non-nil means, allow arguments of macros to be detached by whitespace.
When this is t, `aaa' will be considered as argument of \bb in the following
construct: \bbb [xxx] {aaa}.

You can customize this variable.