Customize reftex according to auctex mode

[Jean Magnan de Bornier]

Hi all, 
I have been trying to customize reftex-cite-format to be "\cite{%l}" when
using LaTeX, and "\cite[%l]" when using ConTeXt.

My first attempt was simply the last line here:

(add-hook 'ConTeXt-mode-hook
          (function
           (lambda () 
             (reftex-mode t)
             (auto-fill-mode 1)
             (LaTeX-math-mode 1)
             ))
(setq reftex-cite-format "\\cite[%l]"))

But this command once given is also applied to latex files; I then tried
writing the corresponding instruction in (add-hook 'LaTeX-mode-hook...
but then auctex has reverted to the latex behavior even for context files.

So apparently I cannot customize reftex within aa auctex mode? Or am I
just clumsy?

AUCTeX 11.85

TIA,
-- 
Jean