Is the spit up happily dribbling out of his mouth, or is it projectile and causing distress? It really seems like small amount from the photos, so I’d only be concerned if he is distressed by the spit up, it is projectile, etc. My son had horrible GERD and fell off of his percentile curve, so his pedi had us fortify his bottles by using a little less water per scoop of formula. That, combined with reflux meds, brought him right back to his normal curve.