I arrived at 1.5/1/175 as my standard dilution. I
can't tell you what it does to the curve, but I arrived at it by trial and error when I was fitting FP4+ to the paper I use. I mainly contact print on graded FB paper and this dilution gives me nicely developed highlights and full shadow detail. My normal development is what I guess you call extreme minimal or minimal agitation. Plus this gives me full(actually a little more than full) film speed. I rate my 8x10 fp4+ at 160, dilute at 1.5/1/175 and develop for 45min(70 degf) in a pvc tube - fully filled with solution. Agitate vigorously for the 1st minute, then 2 inversions at 15min, then 2 inversions at 30min. The tube stands on end between agitation cycles. I usually get a near perfect print at my standard proofing time with great edge contast on what is essentially a grade 2 paper. I develop the paper in DR. Beers at the #4 dilution - which allows me to vary the dilution both up or down in contrast up to 3/4 of a grade.
I've compared negs of the same scene developed in a rotary jobo at a slow speed at 1:1:100 and the difference in edge contrast is remarkable. Altering the amount of restrainer (B) seems to keep the highlights where I like them. Sorry if I'm not more scientific - but I arrived at this based on what I see in the final print.
I've simplified my life greatly by sticking to one film/one paper/and now 1 developer.
Hope this helps.