Thick to thin OR HP migration, how to check how much space will be saved if using -frontend_zero

Is there a way to evaluate if (and how many) zero tracks a thick device has, that would be reclaimed if it's migrated to thin ?

In my case I'm running OR hot pull from thick VMAX devices to thin devices on another VMAX. I'm using the -frontend_zero option (blocks of zeros on source devices are not allocated on the thin control devises) to save space. This question would be also valid for PPME migrations.

Currently I'm using symclone from the thick dev to a freshly bound TDEV and after the copy is done, I can see how much is the TDEV clone target allocated, but this is cumbersome and inelegant, especially with metas. Any other ideas ?