So does that mean the 1020 also has a smaller opening than the 928? It definitely looks bigger
I'm with you here. My indoor photos look great.
Only thing I noticed is my low light shots are grainy when compared to similar 928 shots, but only when I don't use a flash. If I use the flash, the Icon easily exceeds my 928. Honestly not always a fan of flash and the 928 took amazing photos at night without a flash. Hopefully the Icon will be just as good with some firmware updates. The 1520 also had issues with the camera but mostly with video capturing IIRC. Not sure if that's been fixed, but that too sounded like an issue that could be corrected with an update.
Aperture on a camera is the ratio of the lens opening compared to the focal length. If the focal length of both phones is equal (which they are), the lower number will have a larger opening, meaning it will let in more light.
The larger sensor just means the sensor can capture more detail with the light provided to it. The opening in the icon is physically smaller, so it's letting in less light.