Why don't Stereo Fx and Group channels sound stereo?

Hey all - there is probably a basic answer to this, but I can't figure it out.

When I have a group of tracks that are panned wide across the field, why do they lose that sense of width once I put them through a Group or FX channel?

When I create the Group/FX channels, I always create them as stereo, but the tracks definitely lose the sense of width that they otherwise had.

For example, I have 4 background vocals, panned as such - A is L55, B is L25, C is R35, D is R60. This gives the overall BG vocs a nice width, giving a sort of choir feel, and keeps them out of the way of the lead voc up the middle.

Yet, once I put them in a Group/FX stereo channel, they all feel like they're pulled back into the middle. Even if I exaggerate the panning more to overcome that, it doesn't work.

The ultimate result is, despite being able to add group comp/verb/etc, they get less wide and the big choral effect is lost.

What am I doing wrong?