The more important question regarding regionalisation really is how many clubs play in the 'national' leagues, as ABHAS goes on to say.
Country A has tier one of 20 clubs and regionises at tier 2. Country B has two national leagues of 10 and then regionalises at tier 3. From the clubs point of view, regionlisation comes in at the same point. Only the top 20 clubs play in a national league, regardless of how many tiers there are.