How to make character navigate around navmodifiers they are blocked from?

Nonder

I don’t think its working for me, I attach 2 images on with navmodifier set to custom AreaClass and one with same area set to navarea_null

custom area class is has its “draw colour” set to bright purple, in defaults section of blueprint.

one with custom area simply shows a normal green unbroken nav mesh, where as one with NavModifier set to null shows navmesh not covering that modifiers area.

What am I doing wrong ?