I don’t use field activities when doing terminal automation. I use Move Cursor to put it where I want it, then Send Keys to type, since things don’t usually change position on a terminal screen.
One thing I’ve found, at least with our mainframe, is that sometimes it’s picky about exactly where you start typing - so sometimes I use Move Cursor to move to the label and then Send Control Key tab to get to the correct place in the field to start typing.