Navigation modifier volume layers

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Hi, so, for example, i have two modifier volume, which is placed in same position, but have different area classes. First modifier have extent 100,100,100, Second is 300,300,100. My question is have i can make first volume above the second (like layer in photoshop), and what does it depend on? When you add this nav modifier as actor component in Bp, it have checkbox “Use Agent Height”, i don’t know, mb it’s my solve, but i don’t know how setup this agent value.
thx