I agree; Iruru comes across as much more... reasonable in here. They may still be the size of her head, but it looks like she gained a foot to her height, without altering her other dimensions, and underwent a few artistic changes that makes her look more mature (a less rounded face, slightly different hair style, etc).
One of the earliest chapters she shows up in the mainline: https://mangadex.org/chapter/14818/6 (Also, despite the differences in posture, that panel makes her look way shorter than the already not-very-tall Kobayashi.)
Edit: More recent chapter with Iruru employed at the same shop. She's waaaay shorter than the owner in this panel, though not as much in some of the others in this chapter: https://mangadex.org/chapter/178800/9