SmugMug seems to have better display options than Zenfolio per this article.
https://www.smugmughelp.com/hc/en-us/articles/18212296628884-Change-the-display-size-of-my-photos
https://www.smugmughelp.com/hc/en-us/articles/18212296628884-Change-the-display-size-of-my-photos