i think the info your looking for is,the ipr is on the pump it self it is a regulator,it regulates volume. ICP sensor is just that a sensor for the pcm to see what curent presure is. Now at idle on a stock truck in a perfect world 9% ipr dc at 500psi would be great,now with wear on the pump and injectors 11-12% at 500psi would be ok any higher dc to the ipr to mantaine around 500psi would indicate a leak. Now with custom tuning these parameters can be altered to suit your needs and use of the vehicle,meaning if your idling at at 15% dc and your icp is 650-700psi then i would assume there are no major issues and relate it to tuning. Theres nothing wrong with that at all maybe just alittle rough idle,but 15%dc at 450-500 psi would mean theres a problem,now as far as at wot remember the ipr is a simple regulator and 3000psi no matter what the ipr dc is will always be 3000psi meaning 30% dc or 60% dc its all the same as far as load on the pump. In closing with all the different injectors on the market today and different styles of tuning it can be hard trying to compare one build to the next for alot of different reasons,and there really is no major right or wrong answer to this question there for if your maintaining 3000psi at wot your doing ok and your not killing the pump your just not wasting off as much as some one maintaining at 50%. Sorry for long post.