Yes, thanks for the question. It doesn't affect the peak brightness at all.
Our abbreviation of "% as big an effect on your body as daylight" is "% Daylight"...it may be too short. Maybe we should write it as 'circadian effect' instead.
We are trying to nudge people to think of screens and lights as things that have a big impact on how their body works. Not just the sort of aw shucks, let's make it do a little less, but something we can really measure.
And so your example is a great one, because someone with a 13" laptop screen just sees a ton less light than your 4-monitor setup, and we're trying to put a number on that, so we can "fix" it.
Most people would probably think f.lux is only changing their screen (maybe that's all they expect), but our work is mostly on how those screens and lights affect your circadian system.
So when that screen changes your body and circadian timing (and we can measure or simulate it), we are trying to find a way to talk about that effect, which is complicated. But we're trying to do it anyway. :)