Mana and magic is fuelled by belief and worship in Western Shores - there's a high level of religiosity in the general populace and churches for the same (or similar) deity will generate the focal points of the ley lines, which stretch in a network (ie all the Loki churches are connected to each other by ley lines). Clerics are the dominant form of magic user, the Church oppresses all secular magic (wizards and such). Clerics have more power, but are pretty much limited to the kinds of spells relevant to their particular order and which deity they prefer in the pantheon (they can only use one flavour of Ley Line). Wizards can tap any ley line and have a more diverse range of spells (and don't require duties to any particular deities). The distance from a place of worship or a ley line has an effect on the skill you use to power your spells (ie this bit https://www.curufea.com/doku.php?id=roleplaying:hero:ws:casting_spells )
There are Ley Lines almost everywhere in the heavily populated human dominated areas. They're sparser elsewhere. Clerics have real problems if they visit cultures with very different religions - missionary work is almost all about establishing the equivalent of an embassy for their deity, just so they can get their magic working.
I've only run a couple long campaigns in the setting - one where the PCs weren't spellcasters and the other was in the alternate timeline of the Golden Age of the Elves, so sadly there's been no playtesting of this yet.
There needs to be default packages/templates that differentiate secular from non-secular magics - Clerics get easier rolls for more powerful, more limited spells and everyone else is more versatile but less powerful.