In The Helion, in the first 2 measures the harmonies are maj 3rd, min 3rd, min 3rd. In the 3rd measure, it's 4th, 4th, then maj 3rd.
So I'm not sure how you could do this with a preset. In other words, if you set it to the key of Em, and have it do 3rd intervals (which would choose either maj 3rd's or minor 3rd's, depending on the notes you play), I don't know how it would know to do those 2 4th intervals, instead of choosing a minor 3rd.
Maybe that's what you're hearing. Why not just play that intro as 2-note chords yourself. It'll sound the same as what you're after, and it's not difficult. (Unless you're talking about something further on in the song, which I did not look at.)
And without looking at the other song, I suspect something similar may be going on.
Picture this: On a piano, if you play a C & E, you're playing 2 white keys, with one key in between them. Now run that same pattern up the keyboard. Those intervals will all be
3rds, but some will be minor, and some will be major. Which are which, comes from the key, which in this case would be C major, or A minor, depending on how you look at it, or the musical context. A preset can do this for you, as long as those
intervals don't change. But for it to switch to a 4th, as in this song, or even any other intervals, which is what happens in lots of harmonies, I don't know that you can make a preset do that, because how would it know when/where you want a different interval?
And forgive me if you already understand my "piano" explanation of diatonic 3rds.