Due to antagonism from Ca:Mg and Fe.I don't think this should affect the Fe. I assume you are referring to Mg and K interaction which could interfere with each others and where Mg Deficiency (look similar to Fe Deficiency/Pale Growth) could occur due to excess K ? But in your case this is less likely to happen because your K is still not that high. let me know if this is why you wanted to make the change listed in the quote?
I only added K since it is part of my remineraliser.
In the past I had gone as Low as 0.03ppm Fe weekly (though this was soil) in very soft water.
So yeah, that’s why I am considering moving it down, maybe at a later date though.