Right, but is it really as simple as just preserving the chelate here? Seems like if that's all there was to it folks would've been mixing their csmb and macros together with a dash of vinegar all along.
It may be as simple as it sounds: small amounts of phosphate mixed in with a strong iron chelate.
Colin did with Thrive. Now George Farmer and these guys have done it. I'm sure both went through several prototype solutions before arriving at the commercial formula.
Since you've been blending ferts of late, you could easily test your theory with PortalMaster's testing equipment. Forget about N, K, Ca, Mg, and the other micros. Mix a few different concentrations of just phosphate and Iron DTPA. You mix it up, store it for a few weeks. Then send off to measure P and Fe. You know the theoretical input. Actual numbers will be lower than theoretical input due to precipitation. I think you'll find that higher the P, lower the Fe. I suspect a commercial formula like Thrive+ is lower-than-EI in P and there is built-in iron overage to compensate for the minor amount of precipitation.
It may be as simple as that. Colin and George may be reading this and laughing their asses off. Who knows. People have been told not to mix their macros and micros. They listen. I know I do.