When to add more oz to formula

My LO is taking roughly 3oz 95% of the time every 3 hours during the day (nighttime she takes 6 oz in a span of 3 hours bc she’s clusterfeeding)

I’m scared to up it up to 4oz bc she does like to spit up. Not every feeding ,but when she does, it’s a lot.

Should

I try the 4oz or wait until she’s 100% taking in 3oz