Sorry...I assumed we both had the same setup.
I'm not sure exactly which unit you have but it sounds like you have the unit that has two FloodJet WideAngle tips. The FloodJet WideAngle tips are high volume tips and you probably won't get 40 psi with the 2.1 gpm pump.
If you are wanting to switch to flat spray tips, yes, I would recommend the 11004 AI tips.
That 2.1 gpm pump may be sufficient to get 40 psi for 2 X 11004 AI tips.
With 2 X 11004 tips set 20" apart and 20" high you will get a spray width of less than 4'.
You could add one or even two more tips to the boom but then you would definitely need to go to the 3.8 gpm pump which would probably have pump cycling issues with so few tips.
Try two new tips first and let us know how it goes.
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