How to Setup Permalinks for a second, sub folder installation?

I’m trying to setup the permalinks for a second, sub folder installation of wordpress (I will call it wp2). When I select the Custom Structure option (located on the options-permalink.php page) I just want to add /%postname%/ so that the url for the second install would look like https://www.wp1.com/wp2/%postname%/ but what I get is https://www.wp1.com/wp2/wp2/%postname%/??? How can I remove the repeated wp2 folder name in the permalink? Any ideas?