Rope slippage for an ATC / Reverso in guide mode?

I would like to ask if anyone has data on the possible slippage of a tube style belay plate in self-locking-mode configuration when the second climber falls.
I am interested in comparing it with a Munter hitch (or locking Munter).

I have observed slippage with a reverso 4 in guide mode using 8 mm extremely icy ropes.  I climbed a very wet ice pitch in cold conditions, and the ropes became ludicrously coated in ice.  My follower (one follower climbing on twin ropes) weighted the rope, and I noticed the rope slipped a few inches before my hand on the brake strand kept it from slipping more.  I later experimented, and it seemed I could pull significant quantities of rope through the "wrong" direction, and it would only occasionally catch on a less icy section of rope.  Very little force was required on the brake strand to keep it from slipping.  This was still a wake-up call for me, as I had previously believed guide mode to be essentially safe hands-free assuming the device or carabiner not to be touching the rock or anything else that could prevent it from rotating freely, and assuming there not to be two followers climbing in such a way that the ropes could enter the device coming from different directions).  

These are plaquette style belay devices, not simply a tube device.  Difference being the ability to top belay (and other cool tricks).

Not sure about slippage, a myriad of factors would effect that: particular device, rope diameter, wet or icy conditions, etc.

No device should ever be considered hands-free.

I once took a fall around FF1 onto an ATC guide when I fell following a traversing downclimb pitch. According to my partner, around a foot slipped through the device before it locked up. 

Fran M wrote: I would like to ask if anyone has data on the possible slippage of a tube style belay plate in self-locking-mode configuration when the second climber falls.
I am interested in comparing it with a Munter hitch (or locking Munter).

You've posted a vague question and you'll get worthless vague answers.  There isn't one, or even a few, good answers to this because there are too many variables.    

John Byrnes wrote:

You've posted a vague question and you'll get worthless vague answers.  There isn't one, or even a few, good answers to this because there are too many variables.    

I'm asking for people to sheir their data for free so I will leave it up to them to tell me in what conditions they made their measurements. I think I stated what I am after quite clearly, didn't I? Whoever has some data probably can state stuff like rope diameter, device model, fall factor, TPRH conditions or whatever they fancy.

Fran M wrote:

I'm asking for people to sheir their data for free so I will leave it up to them to tell me in what conditions they made their measurements. I think I stated what I am after quite clearly, didn't I? Whoever has some data probably can state stuff like rope diameter, device model, fall factor, TPRH conditions or whatever they fancy.

Oh, you're leaving it up to me?  Well, in that case, it slips like mad.  There, did that answer your (ridiculous) question?