Aspect of BOZ
First Post
Excellent. 
I do think it’s important to retain the concept that the pod denizens are Medium-size with 20-foot reach. First of all, that puts them in the way to a point where you can’t move through their space (since you can move through the rest of the bloodsipper’s space, after all). Secondly, since they’re stationary while tethered, the DM would need to place them in the bloodsipper’s space for the best strategic advantage. A bloodsipper could only attack very big creatures with all twelve, and it couldn’t attack Medium creatures with all 12 even if they were clustered together (and clustering them together would reduce their general effectiveness anyway). Actually, very big creatures would probably not be able to move around in a bloodsipper’s space unless it’s able to squeeze between the pods.
There’s another advantage of the Attach ability – it is not restricted by size, unlike improved grab. It can bite and attach to creatures of any size, even big ones having a hard time navigating the bloodsipper’s space.
Let’s assume a “half-strength” bloodsipper. See the diagram below: each colored box represents a pod denizen, and the line of the same color is its reach. Some squares can be hit by two or even three bites, while some (mostly those adjacent to the denizens) can only be hit by one. Now that’s a hell of an obstacle course – imagine if there were 12 to deal with!

I do think it’s important to retain the concept that the pod denizens are Medium-size with 20-foot reach. First of all, that puts them in the way to a point where you can’t move through their space (since you can move through the rest of the bloodsipper’s space, after all). Secondly, since they’re stationary while tethered, the DM would need to place them in the bloodsipper’s space for the best strategic advantage. A bloodsipper could only attack very big creatures with all twelve, and it couldn’t attack Medium creatures with all 12 even if they were clustered together (and clustering them together would reduce their general effectiveness anyway). Actually, very big creatures would probably not be able to move around in a bloodsipper’s space unless it’s able to squeeze between the pods.
There’s another advantage of the Attach ability – it is not restricted by size, unlike improved grab. It can bite and attach to creatures of any size, even big ones having a hard time navigating the bloodsipper’s space.
Let’s assume a “half-strength” bloodsipper. See the diagram below: each colored box represents a pod denizen, and the line of the same color is its reach. Some squares can be hit by two or even three bites, while some (mostly those adjacent to the denizens) can only be hit by one. Now that’s a hell of an obstacle course – imagine if there were 12 to deal with!