At least in my case, in the iOS app, using “Choose image” fails to record an accuracy value for the observation, even when accuracy is recorded in the image metadata. It would be worth doing a test to see if this is a more general problem, as no-one has been able to confirm either way in response to my bug report.
To ensure precise locations when not using the app, it can be helpful to open another app (such as a mapping or GPS app) to check the the position is updating before taking a photo.