Use OpenType GPOS mark anchors, that should give you enough control over placement of "diacritics" on any glyph.

Maryamsoft.com recognized the fallacy of the mark-positioning notion and cleared the air on that score:
http://typophile.com/node/48495

saleem Ali

I am working on Nastaleeq urdu font it is not contextual alternate are not get what happened MS work .doc file attached the problems highlighted in circle. insert image error if you want see my problem give your email.

Mr Aziz Mostafa,

Plz reply my above problem insert image error that's mentions happening. i am waiting your kindness and guidance.

I have very difficulty in this situation word is overlaping each other. My problems is to see below how i calculate width in volt Single adjustment menu plz answer this problems in urdu first is kay inital and bari yeh fina, lam init, middle hamza and yeh fina Meem init, jeem meddle dochashmi hay and bari yeh fina same as other words so you can see. how i solved and how calculate single adjustment menu table width define. I will be appreciate for your prompt action.
pic

This is a kerning issue. You need to provide kerning between the word that contains the Yeh Barri and the "Space" character that comes before the word, as well as the letters that do not connect on the left like Alef.fina, Dal, Reh, and Waw.

There may be easier ways to do this, but here is one approach to the problem. I make groups of the letters, or letter combinations, that come before Yeh Barri based on how wide they are. When the width of such letters, or groups of letters, is more than the Yeh Barri tail extension to the right, I provide appropriate kerning as needed between the first of the connecting letters and the Space character that comes before it.

The number of such kerning lookups, the type of adjustment, and what context to use in these lookups, will depend on the particular design of your font.