How to remove an iOS contact poster but keep the photo?

I created a contact photo for one of my contacts using my iPhone & in the process it also picked a poster (it actually starts with the poster & then crops/centers the same picture for the contact's photo). I'm not a big fan of the poster, have a few contacts with just the photo (probably created before the concept of poster existed) and prefer the more subtle display when they ring (just a name with the photo in a little circle next to it as opposed to the more obnoxious full photo across the entire screen for the contacts with posters). But I can't get rid of the poster without also removing the photo. Am I missing something?