Text Formatting ⇒ modifying default font-size for Subscripts/Superscripts ?

[mic76it]

Dear all,

is it possible to modify the defaults fontsize and position of superscripts and subscripts ?

I would like this :
$M_{ij}^{kz}$
to look like the following :
$M_{_{ij}}^{^{kz}}$
just modifying a parameter at the beginning of the document.

is it possible to do that?
(I've been looking for that on the net for a couple of days ... unsuccesfully)

Many thanks for any help you could give me.

Regards
mic