Last month was about $3.30 per TB for me. But last month as well as the first few days of this month (which you’re basing the numbers on) have been a little less profitable than average. It fluctuates. $3.80 is from the earnings estimator, which I tune to represent a bit longer term average behavior.
Additional note, I have 2 full nodes like yours that make similar income to the $2.50 you quote. They make a little more, but it’s fairly close. Which just reinforces that more recently uploaded data is more likely to be downloaded. I’ve been meaning to check if I can find out the relation between downloaded pieces and their piece age so I can actually take this into account for the estimator. But I don’t think the node databases have all the required data for that unfortunately. I may implement a best estimate at some point based on comparison between my full nodes and my node with free space.