Try drawing the smaller pixmap to the biggest one, and then to the Texture:
Pixmap imgA = new Pixmap(Gdx.files.internal(back));
Pixmap imgB = new Pixmap(Gdx.files.internal(overlay));
Texture dynamicTexture = new Texture(200, 200, Pixmap.Format.RGBA8888);
imgA.draw(imgB, 27, 27);
dynamicTexture.draw(imgA, 0, 0);
Reference: this other question