thank you for your thorough answer. I just had a peek at a similar thread and had already tried out the code you mentioned there, tailoring it to exactly only the search instance at hand, but didn't have any luck with it. Also, turning off compact mode didn't help, the field is accurately expanded, but no tapping possible. The fun is, when you try a random URL to trigger the 404 page when there is a second, almost identical search form, that form actually IS working.
All the best