Thanks for your feedback!
The reason alien appear closer than resources has to do with the bounding, basically resources require a farther distance to disappear, while enemies just disappear almost as they get offscreen, maybe I could check if they became visible, then if they disappear when they became visible, I could delete them.
That was also somewhat suggested by a playtester, basically different resources and something to use them on, but I thought it would go against the jam theme.