Yep. The BlockBox entity is EXACTLY what I was looking for.
I'm using this item to prevent an exploit where Players can potentially jump across a chasm onto objects that people normally wouldn't be able to jump to in the real world. For example, you wouldn't expect to be able to jump 6 feet between two buildings and land on the 1 inch wide ledge without falling. That is exactly the kind of situation where you would place Blockers.
I hate it when these Blocker features are used overtly to 'channel' gameplay. 'Legendary' really sucked because of this overuse. They should only come into play to prevent Players in subtle and undetectable ways.
I noticed a nice feature about the BlockBox. It stops the Player, but you can still toss junk at it and the junk will pass through impeded and without revealing the Blockers presence. Highly desirable effect. Can't have rocks and crap bounce off of invisible barriers...
Thanks for that info. Appreciated.