Why don't you place the diffuser under the powerhead?
for one, the grass would be in the way and I'd have to have it higher up. I'd also have to bend a new glass pipe for it's different positioning.
but more importantly, it's lined up directly with the outflow of the xp3. the bubbles get thrown down into the the water column and swing towards the back by the flow of the xp3. any bubbles that get close to the surface after the xp3 "throws" them towards the back then get propelled back down into the water column and to the right side of the tank by the powerhead. the powerhead essentially catches all the bubbles the xp3 can't prevent from reaching the surface.
the xp3 and koralia thus work in tandem to keep the bubbles in the column and circulated around the tank. these days I run slightly less than 1bps and have no noticeable algae, the diffusion rate is quite high when both sets of flow are circulating the bubbles. using strictly RO/DI water also helps