I consider a little high as anything between 7 and 10.
I base this off a (single) example of someone without diabetes peaking around 9.
Anything over 10 is moderately high and anything over 15 is very high.
For me the very high is important as it is when I start becoming insulin resistant so I need a higher insulin ratio to correct the high.
Also important to me is why I am going high and how long I have been there.
If Libre says I touch 16 for 30 minutes, I don't fuss.
If I am going up to 13 because I had a pig out on something I have never eaten before, I take it as a lesson learnt that I need to either split my bolus, have more bolus or not bother with that meal again.