Thanks guys - yes, there are 8 in there in total, down from the original 12 I stocked with.
As I mentioned, they do occasionally chase one another - not far, like a 6-12” dash, as if carving out territory or asserting a pecking order, but the other Kubotai typically just swim off out the way behind a plant etc. They occasionally chase the Embers in a similar fashion - not that the Embers seem that bothered by it.
I’ve never seen them stay within the same space, so persistently though - they were there for at least an hour. They were doing it again today (well, I’m assuming it was the same pair), in an open area of the tank, and again neither was even attempting to swim off out of the way. They’re also not pecking at one another in any way, and there is a lot of flashing of sides against one another, which is what made me wonder if it was mating behaviour.
I have rescaped recently, and the rescape was with lava stone rather than Seiryu stone that the previous scape had - which in the previous scape was causing the water hardness parameters to go fairly high. In this new scape with the lava rock, I’ve finally been able to achieve real softwater parameters (<2kH). Though I’ve acclimatised them to these softwater parameters for about two weeks in the holding tank, again I did wonder if this might have triggered spawning behaviour.