Confused about Titan's Bane

Me and a friend of mine played a game of Smite today (duh) and we came across another enemy Loki. Better skilled than me, but his item build was a little different. Me and him have close to the same items, but his was slightly altered. He had a titan's bane, but he already had warrior tabi, jotunn's wrath, and normal voidblade.

If I understand the description of the titan's bane, that means the enemy Loki was trying to give himself 33% more penetration than the cap allowed. So, my question is: Titan's bane states that it gives the attack 33% physical penetration. Does this mean it boosts the penetration you have from other items by 33%, OR does it mean the attack ignores 33% of the enemy's physical defence, OR does it mean that the first 33% of the damage ignores physical protection, and the physical prot/pen calculations are applied to the rest of the damage? It seems to be rather inspecifically worded, which is unhelpful when debating the pros and cons of a build.

A further question that would help us understand this is how does physical protection mitigate damage (offset? precentage?), and how does physical penetration mitigate physical protection (again, offset, percentage or something else)?

There is a cap on flat penetration, but not on % penetration. Titan's Bane is 33% of your targets full protections, so a target with 100 protections gives you 33 penetration then you have your flat pen on top of that.

Went over it on some length a while back:

https://www.smitefire.com/smite/forum/theory-crafting/penetration-1355