Batching problem : more batches than materials on a fully static model

Hi,

I’m trying to reduce my number of batches (or drawcalls) in my GearVR project.
I’m using Unity Free, so no dynamic batching for me.

I have a 3D model I made using Sketch Up, I’ve tried to keep my number of different materials as low as possible to avoid CPU overhead.
The whole model is marked as static (everything static : occluder, occludee, navigation, batching…).
I’m not messing with any material of my model through script (so, no, I’m definitely not making clones of the materials at runtime)

At runtime, I do see that static batching helps reducing the number of batches : the “saved by batching” number shows that the batching magic kicks in.
Yet I have way too much batches, and I don’t understand what goes wrong, but something definitely does : I have a grand total of 50 materials, all using the standard shaders (and changing shaders doesn’t change a thing on the batches side), yet depending on where my camera is, disabling my model can reduce the number of batches by roughly 150 (out of 170). How comes?

Note :
I only have one camera
I only use the standard shader, but they all only use the Aldebo field with the Opaque rendering mode, except 2 materials that use Transparent rendering mode.
I use occlusion culling
I use light baking (no precomputed realtime GI, baked GI with low parameters for testing purposes)

Thanks in advance for your help.

Oh, one thought…
I just remembered reading that having a mesh with multiple materials was bad, but no one ever explained why.

Exporting from Sketch Up tends to do that sometimes… I’m guessing that could be the reason, I’ll try to do some testing and keep this thread updated…