How can I increase the spacing on both sides of the glyph Without closing the property Automatic Alignment?
Why would you like to do this? Why not just set the side bearing of the dotlessbeh to 100?
in arabic fonts We adopt the spacing between the glyphs proportion to the concentration points above or below
The main idea of automatic alignment is to keep the width in sync, but you can have various base glyphs with different widths. In your case, I would add a dotlessbeh-ar.wide with a dotlessbeh component and metric keys like =dotlessbeh-ar+50 on either side. And then, you could use dotlessbeh-ar.wide as base component where you need extra space.
Method does not work and do not do any good … I have many of the marks of different size, is I’m going to produce dozens of the dot-less for it?!
The size of the marks have nothing to do with the width of the base glyphs and the compound glyphs. The dotless glyphs should always have the same spacing than the dotted glyphs (like the Latin A has the same spacing than the Aacute and Adieresis even through the accents have a different size).
The marks are positioned with the anchors. Here is a tutorial tha explains it for Latin accents but it works exactly the same for Arabic marks: http://www.glyphsapp.com/tutorials/diacritics
The method I described would be good if you needed one extra width.
Another way would be to add pos rules for all glyphs that need extra spacing. Add a feature called kern and put this rule in there:
pos @tripleDotInits <50 0 50 0>;
And make a class called tripleDotInits which contains theh-ar.init and other glyphs that need 50 units extra in front. Add other rules and classes for individual extra spacing. You cannot preview GPOS features inside Glyphs though, you will have to test it in InDesign.