Is there a way to report on the maximum value per day that a metric reaches?

Yes, there is some work that needs to be done here. Likely the UIv4 transition will completely change things. "pow" is expected because you're only taking the current value and raising it to a power. Similar to other simpler arithmetic functions like a + b. 

Yes, percent(0) and percent(100) are the easiest, although not most intuitive ways of getting the max and min on the graph as flat lines.