Based on this (Pi chart) https://www.raspberrypi.org/help/faqs/ , the absolute max power consumed by the bare baseboard under “stress” conditions (that normally includes boot) is 1.35A. With screen added this would be 1.82A. If any other peripherals or mass storage devices (e.g. Disks, Solid State memory) are used the power consumption under boot conditions may well exceed 2.5A. As the RPi is a DIY Kit with many configurations it is up to to the person assembling the system to ensure a suitable power budget. If too many peripherals are attached the iPower may be overtaxed during boot, while during normal operation of the basic board with minimal peripherals only a small fraction of the available power is used.
Past that the more the iPower has underload the lower the voltage.
Open a support ticket with us to re-confirm your setup/system.
