How is fortification above 100% used?

[redoubt]

Reading in another very long thread someone stated that a CR54 mob requires 154% fort to not be critt'd or sneak attacked.

Is this correct?

Does it apply the same at low levels? When we are fighting a level 20 mob at around level 10 we need 120% fort now?

Please don't launch into right or wrong about it, that can be in the other long debate. I'd just like to understand the current game mechanics for fortification.

Thanks!

[MrCow]

If a critter has any sneak attack dice, it gains a fortification bypass equal to its Challenge Rating.

• If a CR 1 Kobold Sneak attacks someone with 50% fortification, the Kobold Sneak has a 51% chance to normally conduct a critical hit or sneak attack.
• If a CR 20 Lava Mephit attacks someone with 100% fortification, the Lava Mephit has a 20% chance to normally conduct a critical hit or sneak attack.
• If a CR 54 Sellsword Footpad attacks someone with 150% fortification, the Sellsword Footpad has a 4% chance to normally conduct a critical hit or sneak attack.
• If a CR 29 Earth Elemental attacks someone with 125% fortification, it is still going to have a 0% chance to critically hit or sneak attack, as it has no sneak attack dice.