It is usually higher than the Average. From a mathematical point of view, the more data you have, the more obvious it will become.
The baseline is computed by taking the max value found in the Upper Baseline graph (75% tro 95%), and to that value we add 20% - if that max value we found is 25seconds, adding 20% to it gives 25*1.2=30seconds.
And that is what we will use.
Keep in mind that the Baseline is here to identify issues with the WebSite, based on "known" data. So we want to catch the exceptions here.