A TLS client can not make any assumption about the size of a certificate. Certificates can include images, texts, lists and much more. Assuming that a certificate has a certain size is going to lead to problems in your software.
Certificate with many, many subject Alt Names
This site presents a certificate with a very long list of subjects. The certificate in itself is over 20 kbytes.
This certificate is valid.While most certificates doesn’t have this amount of subjects, there are certificates that have a lot of subjects that a client needs to validate. Check the certificate of https://youtube.com as an example.
Make sure your client goes through the list and validates the site properly.