Years back, I was at a conference.... at one of the sessions, the Extension fertility specialist reported on research they had done using only nitrogen in soils with very high phosphorus levels.  They applied liquid N in a 2x2 placement, with no other fertilizer.   The theory behind it is the nitrogen will acidify the immediate zone where it is placed, making the phosphorus in that zone more available.  It may be something you want to look into.

There are guys that are cutting their liquid starter with water.  The goal is to get the liquid fertilizer rate down to, say, 3 gallon/acre.  So, using 3 gal/acre liquid fertilizer + 2 gallon/acre water, and it can still be applied at 5 gallon/acre. 

To answer your question, if you have high phosphorus soils and still want to use a pop-up fertilizer, you can use a lower phosphorus analysis fertilizer.   

The question that runs thru my mind.... if you have low soil potassium levels, are you addressing that in another way?  My opinion is that if you have low potassium levels, you can't address that with starter fertilizer.  You can't get enough on with starter fertilizer to address that issue. Do you have another way to address it?