Caltech has 25th percentile of admitted students 34 ACT, so I would assume it would be difficult to get in there with a 33. If you don’t have a hook and particularly if you belong to certain ethnic groups, you usually need higher than the average SAT/ACTs for a school. You may need other things on your application, but I wouldn’t say the difference between 33 and 36 is insignificant for top schools.