I have two ways I've been going about this.
1 - dissolving hexagons, keeping any at least 3 contiguous hexagons in size. Any more than 20 hexagons in size need to be divided into being at least 3 contiguous hexagons in size. I've used the PointClusterer transformer (on the centre points) when I had only 2 large polygons that needed to be divided, however, when I have over 12 polygons it's not working so well (perhaps due to the irregular spatial distribution and oddly-shaped polygons).
2 - I've looked at trying to divide the polygons directly, with less success (trying to determine the length and width didn't work so well with the irregularly-shaped polygons from the dissolved hexagons).
Does anyone have any idea of how to make either method work, or have another idea of how to do this?