I am sure you can. It sounds like your system is pretty much set up as it is.
I am not an expert, as I have only had my Iro a week now. I am still trying to dial in things, but for right now I am keeping everything default to see what happens.
There are just some things that are possible (based on brand) to swap the nozzles to dial in your coverage.
What I would do in your position (being a non-profession, homeowner type) is based on your catch cup measurements (perhaps repeat, or test other areas) is create a custom nozzle for 0.3 in/hr and select those. The standard for the rotor type is 1"/hour. However, this will not get you to where you want to go, and this seems like it would triple your cycle time.
That is where the above information, changing a nozzle to get closer to the 0.5" hour or what have you.
Also make sure (as stated above) that you have the correct soil settings. perhaps some screen shots of your program would help.