Binning operation spatial index optimisation for grid coordinates

[prayner]

I have gridded maps of europe that I want to display using the binning operation. I currently use these values to show polygons aligned.

For 4km2 bins, i use gridSize="0.05", gridWidthHeightRatio="1.5".

For 30km2 bins, i use gridSize="0.35", gridWidthHeightRatio="1.5".

For 10km2, I use gridSize="0.12" gridWidthHeightRatio="1.5"

However, for 10km2, i am only displaying less than half of the 10km2 grid coordinates (see the first screenshot). This is very inefficient, so I am trying to figure out how to get one polygon per coordinate. The closest I've gotten is using gridSize="0.9999" gridWidthHeightRatio="1", but this won't show all of the polygons (see empty lines in polygons in second screenshot).

Does anyone know how to calculate this?