The point with these interpenetrations is not necessarily what's useful but what's recorded as happening in battles where we have the information. Sadly, in a lot of cases, troops don't seem to have done what we think would be a good idea.
With a massed Bd/Bw combination, I think the idea is generally to place the Bw in front so they can shoot at enemy. To get them away from the enemy and allow the Bd to do the fighting, you have to pull the Bw back through the Bd. And yes, if you have irregulars it'll be expensive in PIPs. Otherwise, if you leave the Bw in the front rank, and if they survive to recoil, they'll pass through the Bd and provide support from behind.
Which army?