I don't understand, when I lower voltage, my I/s falls from 168 to 147 and Sol/s falls from 315 to 275, but my Shares per second, for what I receive payment, don't change. Does it mean that difficulty of share also vary and I will get less money or not? Is hashrate more valuable than shares per second?
It can take a while after you make some changes to see it reflected in the pool. In my understanding hashrate is what you're looking for, a same share per sec doesn't mean same payment since difficulty of the submitted share may be lower/higher