plotting - How to control the relative sizes of graphics combined with Inset

I created a two grids like this

height = 125;
cb = MatrixPlot[
  Table[Mod[i + j, 2], {i, 1, 2}, {j, 1, 8}]

  , ColorFunction -> "BlueGreenYellow"
  , ImageSize -> {Automatic, 2*height}
  ]

p1 = MatrixPlot[
      Table[1, {i, 1, 1}, {j, 1, 2}]
      , Mesh -> True
      , ColorFunction -> ColorData["DarkRainbow"]
      , ImageSize -> {Automatic, height}

      ]

If I combine the two with Inset, I get

Graphics[{First@cb, Inset[p1, {0, 0}]}]

What should I do if I want to cover the top-left two squares of the yellow/green grid with the red grid?

(I know I could redraw the larger grid with the color of some squares changed. But I want to know how to do it with Inset.)

---

Update, after trying to play with the parameters of Inset, I have found some appropriate parameters that works. But this takes a lot trials.

Is there a way to keep images with their "absolute" size when using Inset?

Manipulate[ Graphics[{First@cb,    Inset[p1, {x, y}, {Left, Bottom}, {Automatic, w}]},   ImageSize -> ImageDimensions[cb]], {{x, -0.1}, -0.5,   0.5}, {{y, 0.8}, 0.0, 1.0}, {{w, 1.4}, 0.5, 2}]

Answer

Maybe not an answer

I think that Inset[] is not what you need.

This is what is happening when one resizes a graphic with some Inset[] without the fourth argument :

If you need a layout that doesn't change when resizing, you can use the 4 arguments form, but I find it a way easier not to use Inset[]at all :.

Like this :

height = 125;
cb = MatrixPlot[
  Table[Mod[i + j, 2], {i, 1, 2}, {j, 1, 8}]
  , ColorFunction -> "BlueGreenYellow"
  , ImageSize -> {Automatic, 2*height}
  ];  

p1 = MatrixPlot[

  Table[1, {i, 1, 1}, {j, 1, 2}]
  , Mesh -> True
  , ColorFunction -> ColorData["DarkRainbow"]
  , ImageSize -> {Automatic, height}
  ];

Graphics[{cb[[1, {1, 2}]], Translate[p1[[1, {1, 2}]], {0, 2}]}, Frame -> True]