Amby baby hammock (reposting)

Hi all! I posted this in a different section and no one was able to shed any light on what I'm doing wrong. I'm hoping to find an Amby expert here.

This was what I posted in the other thread:
I am using a second-hand Amby hammock as a cot. It didn't come with any instructions, although the ebay seller kindly drew us a picture to show how to put it together.
We bought the hammock because we're staying with my parents for eight weeks, then heading back to Vietnam, so we wanted something portable and not too pricey.
The problem is Poppy keeps sliding down the hammock, ending up squashed into a semi-sitting position, with the hammock tilted into a chair. We put her in the middle of the hammock and I don't know how she manages to slide down. I'm too scared to put her any further towards the head end in case it tilts the other way and she slides head-first into the other end.
Does anyone else have this problem? Am I doing something wrong? The hammock doesn't tilt when she's not in it and it looks perfectly balanced when we do put her in it. Maybe Poppy has a unique downward bum shuffle that we haven't noticed.
I sent an email to the official Amby website on the weekend but there's been no reply yet.