Placing pictures on a scale from happy to not happy

I work on an application that allows users to tell their story of their experience in health and social care. At the moment, that's an entirely text based affair. To try to make it easier for people with varying levels of communication difficulty to also tell their story we're working with a third party to enable users to include pictures where their position indicates how happy or not they were with certain aspects of care.

The way this works is simple, the user drags an image that they care about from the bottom tray of icons (not shown) and places it on the story area in line with how they feel about it:

^{download bmml source – Wireframes created with Balsamiq Mockups}

Depending on communication level, the user can also type as much or as little text into the area as they want ending in a patchwork of images and snippets of story (or explanation).

My problem (and question) is simple - should "HAPPY" and "NOT HAPPY" be the other way round?

The reason that it's this way round in the initial ideas is that the third party use this system physically in person and that's the way round they do the scale. However, I'm very used to seeing scales going from negative to positive left to right and this feels backwards to me. Is that a valid concern? Should I even be comparing this to rating scales?