I played a bit this morning and thought about this thread.
It seems like I am softly touching the soft part of the roof of my mouth a bit behind the front teeth when I’m playing legato and the tongue seems a bit looser, whereas staccato or hard attacks are behind my front teeth.
I don’t know if that’s a recommended method, but it’s what I’m doing, FWIW. I do feel like I have a pretty good ability to play legato–I do tend to gravitate a bit more towards softer/lyrical stuff most of the time and don’t have a lot of time to play music.
Good luck, hopefully more folks chime in and you’re able to make some progress on this.