Ok thank you jonathan for your light, I understand now and will try your way.

I've got an idea and you will tell me if it's worthwhile, that would use the tuning wizard.

I would like to "create" a tuning wizard which would help me fine tuning my top layers by observing each top layer at different flow tweak value relative to Z height. I've got the idea and the object, but I don't know how to "program" the wizard.

Here's the object:

Each "cube" (not a cube but let's say a cube for more ease of use) has got 3 more layers (of 0.2mm) than the previous one. The height increases by 0.6mm between each cube. The height of the first cube is 0.6mm, the second one is 1.2mm...and so on. This way, I was thinking that by counting each cube from the beginning, I could find the height of the best looking top layer and enter this value into the flow wizard tuning (don't need a ruler), which in return would give me the value to enter in the flow adjust (flow tweak).

For example, if the 8th cube has got the best looking top layer, I do 8x0.6=4.8, I know the best top layer is at 4.8mm from the base, so I would use this value in the "Best Z [mm]"

I think it can be useful to get a perfect top layer with only one test print. But I don't know how to create my own tuning wizard (I guess I have to use <tuningval> and "Every N layers" but I really don't know how to do that.) If you, jonathan, or someone else could help me to create this, I would be very thankful.