Later Germanic shield bosses

[Paullus]

I've been mulling over the question of Germanic shield bosses from the 4th-6th centuries lately, specifically the sharp conical examples. Obviously this was of offensive use in combat, but why would the Romans, Persians, Celts, Iberians, etc etc stick fairly strictly to the traditional rounded boss? Anyone know? Could it have something to do with the lack of armor around the end of the Western Empire? But a focused pressure point would have a lot of value, armor or no I would think. Was it a simple cultural thing? <p></p><i></i>