I assume you are on Aperture Priority, at f/7.1. You point your camera to the sky to get the in-camera's suggested metering for the sky, that is the correct exposture your camera shows you so you don't underexpose/overexpose the sky. That is metering off the sky using your camera's metering system.
I would suggest the following procedure to achieve consistent results. Set to manual mode using the metered shutter value and the aperture (f/7.1), while leaving the flash to auto. The flash would correct for the lack of ambient light/backlighting on the portraits. Plus and minus power on the flash when necessary. You would realise that using a manual setting would prevent your in camera meter from running loose and choosing whatever exposture it likes. Flash control on the flash unit also becomes more easy.
Tweak the manual settings accordingly to changing situations.
I do this for my events too. By setting my camera on manual, say 1/100 at f/4 depending on situation, I let my flash compensate for the lack of light. This way, I can be sure that I don't get subject movement. Moreover, you will notice that plus minusing flash power makes a difference. I.E. more control.