Small armour pieces only benefit from a percentage of the glyph's enchantment. Apply that glyph to a shield, body, legs or head and you will get 100% - the 340 max magicka.

You get higher numbers if you use stronger glyphs in general, but they can not compensate fully. Chest, Head, Legs and Shield are the only parts that gain what the glyph says it gives.

You can wear armor with infused trait, so you gain more from glyphs though.... it is just most commonly used on Chest, Head, Legs and Shield rather than on the smaller armor parts.