Unfortunately, you can't customise bench spots as particular positions. It would be a good feature though.
Regarding waivers, you appear to be somewhere around the middle of the pack for priority, hence players sometimes going elsewhere. Six ahead of you, currently. You'll move up the list the fewer moves you make.
There's lots of different reasons people might pick up and stash a player though (depth, bye week cover, strength of real-life opposition, emerging (yet not quite there) talents, etc etc), rather than it being out of tactical spite