My UVs are not in the same scale when I apply 'Average Island Scale'

I cannot make the UVs the same dimension, they shrink when I apply Average Island Scale. Is this behavior normal or is it my way of thinking?

Here's the steps to reproduce the problem I found:

1. Start a new project, default settings, and recreate the mesh in photo 1, also apply the same Seams.

2. Using project from view or cube projection, create the UVs for the front and side.

3. You can see the UVs match the height and are at the desired scale.

4. Apply "Average Islands Scale", the uvs get's squished, and there's a clear difference in scale.

5. If Textured, you can see visually the difference, how is that "Average Islands Scale"?

My problem was that, in a project with a object, I had multiple separate pieces, so I unwrapped it okay, with correct seams and everything, and needed to average the different islands, but if I apply the "Average Island Scale", it reproduces the same effect in step 4, it squishes and break the UVs proportion. And yes, I am well aware that objects out of scale 1,1,1, give errors, my objects are always have applied rotation and scale.

I am a fan of the Textools Add-on for Blender, but it seems that the function "Apply Texel Density by Scaling the UVs to match the ratio." gives the same result as Average Island Scale.

Finally, my question is, this effect is clearly undesired, shouldn't the Average Islands Scale take into account the dimensions? Or is it normal to consider angles and geometry when Averaging islands?