Not an expert by any means, but I can bottom rear shocks easily by kicking down on the pegs. However, they very rarely bottom when riding a section. I have the shocks laid down a bit, and lengthened to 400mm (centers) I use 50lbs springs and have reduced the damping both ways to suit. The swinging arm runs in needle bearings, as opposed to silent block which must affect action, even if only marginally. This setup works well for me, and finding grip is not an issue.
Trouble with moving shock mount back is its effect on steering (hence lengthening mine, I have also dropped forks by 20mm)