I agree with your assessment on hunting open areas with decoys; I do feel that they help.
I typically use the combination of a 1/4 or 1/2 strutting jake with some sort of upright-type hen. I actually use a DSD leading hen.
Two reasons that I would prefer an upright-type hen when only using one hen decoy:
1) Better visibility in the terrain I hunt, and the better chance of pulling in birds from further distances.
2) I have had a number of times, where the hens come into that hen decoy to challenge for dominance, and pull in toms with them... Maybe a feeder would accomplish the same thing, maybe not.
Although, honestly, I doubt it will make a difference what brand, posture, etc., of decoys you use... Given the right circumstances, most times decoys and calling together will either work, or not...