Clarifying vulkan glsl std140
The block should total up to 8320 bytes.


No, it shouldn't. You use a uint[16] array. Well, std140 layout makes it clear that the array stride for any array is always rounded up to the stride of a vec4. So that array takes up 256 bytes.

You should instead use a uvec4[4] instead, which you would index from like a multidimensional array.