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AO Bake problem intersection

polycounter lvl 5
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X3KJ polycounter lvl 5
Hi guys,
I have a problem when baking my AO in max. Let me shortly explain my workflow:
I use keyframes to explode the HP model. For the Lowpoly (which is all fused together) i use Editable poly modifier for AO and Normal Positions.

Now, the "HQ" model isn't the regular Sub-D model that is often used, but rather a beefed up LP model. I add mainly surface detail (e.g. rivets, bevels,etc) to the Lowpoly and increse roundness of all things with curvature.

The reason for this is because they are tank models with realistic proportions/sizes, so everything is hard edge stuff. Due to the many 90° edges and small texture space an edge uses i dont do smoothed edges on the HP.

Now to the problem:
The tank models mainly consist of large even surfaces with small details added to them. The small details are not joined with the main surface to save polygons.
Now when i bake the AO, i get a very harsh transition from black to white around every object that is intersecting. The white from "inside" the added geometry is often visible and creates ugly transitions in the texture. Here are some extreme close-ups showing the problem wtih ad-hoc textures.
2014-08-14_00001nusqj.jpg2014-08-14_00002teslv.jpg
Here is a scene to show what i mean
aojag6iojp.jpg
green: floating object slightly above the "HP"-plane
yellow: floating object sits directly on the "HP"-plane
red: floating object intersects the Plane slightly
box: geometry is fully closed (has backside)
cylinder: geometry is open at the bottom (no backside)

green box is the only way to prevent the "lighted inside" and harsh transition in this case.

So far for me the only way to fix this is creating a seperate AO model for everything so that the floating model has a backside and sits slightly above the main surface. However this is extremely time consuming and laborious (and annoying). Handpainting is also out of question, equally laborious and needs to be done everytime something changes.
Can anyone of you guys think of a way around this?

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