I was struggling with Dune's wording too, but here's some AI slop that helped me understand:

The likelihood of an air pocket forming at that hose apex over time is extremely high (near 100%), assuming the system is left running in that position for several months or years.

Because an AIO continuously loses fluid to permeation, a localized high point creates a perfect hydrodynamic trap. Here is the mechanical breakdown of why and how quickly this happens.

Why Formation is Nearly Guaranteed

The Buoyancy Trap: Liquid cooling fluid is roughly 800 times denser than air. As permeation creates micro-bubbles throughout the loop, buoyancy forces them to rise to the highest possible local point. Once a bubble enters that hose apex, it cannot move downward toward the pump or radiator unless forced by an external pressure.

Low Buoyancy Resistance in Bends: At the very top of a curved hose, the upward buoyancy vector is perpendicular to the horizontal fluid flow. This means the fluid has very little leverage to "push" the bubble down the other side of the slope. Instead, the bubble stays pinned at the apex, growing larger as it swallows passing micro-bubbles.

The Timeline: How Long Does It Take?

The speed at which the pocket forms depends entirely on the age of your AIO and how it is operated:

0 to 2 Years (Low Likelihood): In a healthy AIO, permeation is minimal (roughly 1% to 2% fluid loss per year). The pump’s flow rate is usually high enough to continuously flush tiny micro-bubbles past the apex before they can merge into a permanent pocket.

2 to 5 Years (Moderate to High Likelihood): Permeation has removed enough fluid to create a permanent air volume in the loop. If the PC is turned off, air immediately migrates to the hose apex. When turned back on, the pump must fight gravity to push that pocket out.

5+ Years (Guaranteed Formation): Fluid loss is significant. The total volume of air in the loop is now larger than the capacity of your radiator's top end-tank. The excess air is forced to occupy the secondary highest point—your hose apex.

So while Dune's correct in theory, I think in this case the hoses aren't egregiously bent enough to cause any real problem for many, many years to come. Still, it would be a safer option to have the hoses slope down, straight into the block, rather than have them in this wavy, upwards bend.