Input layouts are stored in input layout objects, not in constant buffers! An input layout is valid for any number of primitives (if it works for 100 verts, it will also work for 1000 verts).
the Constant Buffer that has the input element layout for the shader
What are you putting in this constant buffer, and where does the magic number of 178 come from?
It's the size of the buffer in bytes. For a constant buffer, this should be the size of the cbuffer structure defined in the HLSL code. For an index or vertex buffer, it's based on the maximum amount of vertices/indices you want to be able to put in the buffer times the size of a vertex/index.
in the Buffer Description that a ByteWidth represents width of bytes returned