Nice builds. I see you've fitted three blades supporting the ducts upstream the propellers, working as an intake stator.
Have you tested a "twisted" version of those stator blades ? A counter rotating pre-swirl, would increase the propeller efficiency (post swirl -wake- minimization) , at the same time that would .. let's say, homogenize the perturbed incoming flow.
I also see the ducts section is cylindrical. That allows for tip vortex minimization but, I think, it does not help too much for thrust. May be a Kort type duct, together with the stator swirl blades could help more.
Would have to make some numbers. Many times the scale of the ROV results into odd results.
Are those the standard Graupner propellers ?
About the graphs: If I've understood them, looks you've got a lot better "astern" efficiency.