With the vastly improved brightness available in most projectors now I'm less inclined to recommend an A-lens for scope screens unless you're pushing the boundaries of screen size and need maximum lumens, especially if you have a projector with lens memory like the X7000. The X7000 will light up a 130" scope screen with ease provided the room is light controlled and the throw distance isn't out of range.
When you zoom to fill a scope screen with a scope image you're projecting black bars above and below the screen i.e. your projector isn't putting those pixels to effective use, it's trying to project blackness. When you use an A-lens you set your projector to anamorphic stretch i.e. it will chop off the top 12.5% and bottom 12.5% of the image that comprise the black bars, then stretch the remaining image vertically so it's projecting the image using all pixels - the image then passes through the A-lens to stretch it horizontally so it displays correctly.
When you project a 16:9 image on a scope screen you'll have black bars either side, no matter whether you're using an A-lens or zooming. The projector won't be trying to project an image on those black bars.
Like nearly all current HT projectors the JVC is native 16:9 - you can switch between aspect ratios by zooming i.e. you'll have two settings in lens memory. This just requires a little care in your set-up to make sure the throw is right for both i.e. the projector isn't too close to or too far from the screen.
Going with your speakers behind an AT screen, IMO the only potential issue with having the screen edges close to side walls will be reflected light if you have light coloured walls.