You've been given pretty good advice, and I'll go just a bit further with an explanation. If you keep the tines up just a bit, what you grab will do a good job of grabbing more and then you won't need to have the tines on the ground that much until you go back for the final clean up.
Keep your eye on the rake's progress, however, because when your tractor's front end goes down in a depression it will lift the rake up even more, dropping your load. You can avoid a lot of that by anticipating it happening, and lowering the rake a bit for just when you go through the depression and then lift it up a bit again after you level out.
After doing it a few times, you'll see what I mean.
If you lengthen the top link, you'll have the tines angled more toward the back, and not aggressively digging into the ground which would allow you to keep the tines pretty close to the ground, and small stumps should not be a real problem as the tines will "skip" over them without much fanfare.
I use a landscape rake this way a lot, and am happy to have it. Of course, the boxblade is probably one of my most used, and versatile attachments, and you'll be glad to have one of those as well.
John
