Glyphs

leandro.800ub17_ESO

I have some questions about Glyphs. If i use a glyph of any king or example +29 stamina on a item i only get like +19 or less but i also gotten the full +29:

Is this a % change to get the +29?
Depends on the item level?
Depends on type of item (stamina only applier to heavy gear?)

WhiteQueen

Full armour gets the full effect. Head, hand, foot and shoulder armour gets a partial effect. If you apply the "% increase" trait, you get more.

leandro.800ub17_ESO

I have gotten the full effect on head so that's why i am confused