According to Michael's frequency tables, Enter is between w and b ... Mmm that's an idea.
What I was trying to say was that it's right down there in QXZ territory, not up in "should be on a thumb" territory. I think if entering data (numbers etc) then we use enter a lot, but if writing text we don't. If coding, then a lot more. I think Michael used formal text, informal text and code to get his frequencies, so given that code would have pushed the frequency higher, in normal text it will be very low... certainly in modern word processors, only for paragraphs not end of line.
there's also a high chance of multiple Enters hit consecutively, and that's even worse for the pinky. that's how i probably hurt my right pinky on keyboard at work.