I use the Zoom H4n when I want really good sound quality compared to the awful laptop built-in sound card. It seems like the audio clips if I turn it to 100 on the H4n. What is really the 1:1 ratio, so that maximum output from the computer will give maximum output on the Zoom H4n? (So it doesn't clip, and doesn't stay way below.)
The level you need to set on the H4n would depend greatly on the signal level coming in from the computer and may even be affected by the type/length of cables in between. As with any other recording device you will need to experiment a bit to get the levels right.
First turn the levels down to a point where they are not clipping. Record the loudest thing you will be working with and find the loudest part of the recording. Turn up the levels a bit and record just the loudest section again. Repeat until it clips and then turn it down just a bit. This will get you a safe recording level for the loud stuff.
If you are also recording quiet stuff you can either adjust the levels accordingly or add a compressor to regulate the levels a bit automatically.
You will run into a similar problem on the output from the H4n to any other device. Some devices will accept higher levels than others without clipping, and the type/length of the cables used will still have an effect.
Unfortunately, there is no way to find the level you seek without experimenting.