# How to increase vertical Nav Mesh detection for AI Actors? Using Default Query Extent?

For my swimming AI, I wish to use a Nav Mesh, so they may avoid obstacles and swim up and down - preferably.

I figured I should try to solve this with a nav mesh, since UE4 has kindly implemented it for us.

To avoid having the Enemy Fish stick to the "ground" of the map, I would have to increase the Query Extent, which is testable with a Navigation Testing Actor (see images below).

So what I did:

• Add Nav Mesh Bounds volume;
• Add AI Actor with Character Movement Component;
• Increase Default Query Extent in Project Settings (Engine > Navigation System).
• No Profit?

Increasing the Default Query Extent, under Agents, increases it along the positive and negative Z-Axis, which is unfortunate, since I would like the AI to prioritize the bottom Nav Mesh surface.

I have attached two screenshots showcasing the "bad" behaviour, which I would like to circumvent.

The blue Bounding Box, showcases the Extent, which is scaled in both directions, vertically. Preferably, I would like to move it down, relative to the Nav Agent.

To hit the point home, here is what happens when the enemy swims underneath some platform (For simplicity, being the cube):

So my question to you good people is: how would I lower the Nav Mesh detection, without increasing the actor size, or something rather silly. Is there a clean way of having the "Enemy Fish" ignore the top platform as much as possible, without using a Nav Modifier Volume ?