Once and for all - Landscape "Mapping Scale" - what should be the value?

I’ve created a landscape with a material, and I’ve used LayerBlend nodes together with Landscape Coords (and texture samplers of course).
I’ve been using multiple 4k pbr texture I got online, yet they all look poorly; and although possible some of them are poor, it’s unlikely they all are.

I tried to look online and found some places suggesting the LandscapeCoords node should have the “Mapping Scale” property equal to the landscape dimensions.
But what does that really mean? The overall resolution? if so, mine is 757x757, which is way too big number for that (and I tried it, it looks even worse).

What should actually be the value of the Mapping Scale, and if needed, how do I find it?

Just eyeball it. I start with a 7, then plug to a multiply with a Scalar for Master Tiling.
Create the material Instance, Apply to the landscape. Create and fill a layer. Mess with the scaling until it looks decent.
If you multiply by whole numbers you can then simply…

7x2 = 14 - change Landscape Layer Coords to 14 manually. reset scalar to 1.