Well, for this we should see the difference between Mana Sense and Magic Sense.
Magic Sense is the ability to Sense the currents of the world.
Magnetic flows, shifting lava, falling water, rain, hot and cold fronts, even the pressure of an overcast sky, the wind and its flow as well.
Everything is turned into numbers, a value of each input. This allows those who use it to gain a large amount of information.
It's limit however is how much magical ability someone has-their range of data collection; and their ability to sort through that information.
Mana can be said to be the lifeblood of the world. It permeates everything.
Magma and lava have a feeling to it that lets users of this skill to Know what it is made of; this allows the user to tell the difference between the two.
To someone with the ability to sense Mana, they can tell what everything is naturally{in nature/it's nature}. This also ties into the ability to predict pathways.
Granted, while powerful, it's your focus that allows you to get deep information.
The mechanic behind this is simple, you are essentially spreading yourself. Your mana shoots out along pathways, and learns from the World's Mana what you want to know.
This is also why focusing on something that relies on very specific pathways for mana to flow is a bad idea, as a magical being, you have too much to simply focus on it.
Not surprisingly, Your line's Promoted forms are a lot tougher.. You simply don't have the skill for it right now.
Here's another fact, Selene is capable of hiding from your senses, so MCM is a thing. That, and being unable to tell anything about that inlay's composition is more a fact of it's make and energy system. And these Shadows aren't quite running in-sync with mana..
I suppose if you want a simple visualization, think a tree's branches, with the User at it's center.