You're quite right: the distance between the rings determines the actual change in windage or elevation for each graduation on the dials and Winchester's instructions for the scope detail that.
They would have had to make a "dog-leg" front mount to attach to the sight base.
Of course what they should have done was adopt Parker Hale's suggested mount which would have placed the scope overbore and allowed their precious charger loading, but probably "military mind" at that point thought it better not to introduce any overhead mounts lest their wisdom in previously selecting offset mounts be exposed.
And of course it would have meant removing the issue backsight; "most irregular"!