I am not able to make this question understandable enough without a screenshot which shows the dropdown, as I haven't been able to find any reference to what this dropdown is called. This dropdown defaults to 32-bit Exposure with each new file opened no matter how much I try to change it - option click or save workspace or fruitlessly searching preferences for some tiny checkbox I might have missed.
However I am certain that CS4 allowed this to default to whatever I wanted - which in my case is document file size - handy when there are many layers to a file blowing out the file size as it shows the original size and layers combined size.
Can anyone suggest how I can make this default to file size permanently.