Can your upstream be too low?

I have seen this question come up a couple times, and I think there is some misinformation floating about. CableLabs officially states the requirements here. However, reading through them, I can't see a definite answer. This site here states the minimal is 8db. Other sites say 35dB.

Way I see it, the upstream power level is negotiated between the modem's in a given area and the amp. Working with the (CMTS), the amp adjust each upstream(US) channel level to maintain a constant US signal to noise ratio(SNR). So, as long as your US SNR is good, the US power level is secondary. However, since a low upstream is more susceptible to US SNR ingress, many cable technicians prefer it to be in the 40's.