Has anyone got any thoughts or advice about the Input Level control on the Edirol R-09?

I recently used mine on a local history project and recorded an interview with an elderly neighbour. My mate, who was the interviewer, sat in one chair and the interviewee in another about 1.5 to 2 metres away. I placed the Edirol on a coffee table midway between them and about 1.5 metres in front of them.

When I came to play the recording back, after downloading to my computer, I found that the elderly lady's voice was perfectly audible but a little faint. I turned the computer speakers' volume control up as high as it would go but could still have done with a bit more volume.

I subsequently played around with the Edirol's 'Input Level' controls, while recording the sound from my TV. I found that, even with the Input Level set at maximum ('30' - whatever that is) I was getting no clipping when the unit was about 1.5 metres from the TV with the sound at a comfortable level for my hearing. I had to turn the TV up quite loud to get any clipping at all, hence the lower settings for Input Level (<30) seemed superfluous. Am I doing something wrong or should I always have the Input Level at max except when recording Heavy Metal Rock (very unlikely!) or something?