Grettiron, Failed lower position generally means lack of ROM into internal rotation, extension, and/or adduction. This can be due to muscular length issues or a host of other mobility deficits. IMO, the Apley's Scratch test is a quick and VERY general test to show overall shoulder mobility and can help guide you in a direction to find more specific limitations. To try and find specific limitations from the test is not in your best interest.
So for the example of failed lower position, if you do not want to get more specific, I would just say to work on your shoulder ROM and mobility into internal rotation, adduction, and extension.
mmllcc, as for the winging and if you should hold the scapula down to stretch it, I don't feel that is your best option. Without testing you myself, it is impossible to give an exact reason why you are winging, but generally it is a weakness in serratus and scapular retractors and I would rather address that than try and increase mobility/stretch in the manner you are stating. Stretching would be beneficial for pec minor and other surrounding musculature, but IMO it is more beneficial to strengthen the musculature that will help hold the scapula against the rib cage and not have an external force causing that position.