Don't shout, whisper?

Most speech-therapists and lipreading tutors will use voiceless speech (silent speech) in their lipreading training.

I've asked them why they do this. The answers so far:

1. In lipreading groups, some participants may have some hearing. If the tutor uses normal speech, the participants with some hearing have an advantage over the deaf participants. Using silent speech makes for a more equal playing field.
2. Many therapists / tutors include normally hearing partners in their groups. By using silent speech, they normally hearing partners experience what it is like, to be deaf.

But many (all?) speech therapists / tutors who train lipreading on a 1-1 basis, also use silent speech. Why?

I don't know.

Maybe because many clients (still) have some hearing, and exercises would be too easy if they could hear & see what the therapist / tutor says?

On the other hand, it makes the activities more difficult, more frustrating, and also: less realistic. In real life, people WILL use their residual hearing!

From my perspective, therapists should teach lipreading learners how they can combine the two channels (ears, eyes). Some things can be heard, some things can be seen.
If exercises are too easy for a particular learner, when the therapist / tutor uses his/her voice, then the therapist can add background noise or white noise. Or s/he can ask the learner to turn down the volume of the hearing aids or CIs. But I would not recommend to use voiceless speech!

A related question:

• How do voiceless and whispered speech compare to normal speech, visually? Are the mouthpatterns the same? No, because in voiceless speech, the vocal cords don't vibrate. Are there other differences?
  When whispering, does the speaker move lips, tongue and jaw more actively, to compensate for the lack of volume?
  I've tried to find research on the 'lipreadability' of normal, whispered and voiceless speech. So far, no luck. I've also looked for the visual characteristics of normal, whispered and voiceless speech. Still searching. It does seem that whispered speech is spoken more slowly, and that consonants last a bit longer compared to normal speech. 

All books, websites, flyers etc. about communication with hard-of-hearing and deaf people repeat the advice that the speaker shouldn't shout. Shouting changes mouthpatterns and makes lipreading more difficult.

Maybe whispering makes lipreading easier? Maybe we should have buttons, t-shirts and banners that say: 

"I'm hard-of-hearing / deaf. Don't shout, please whisper!"

True? Not true? 

Anyone who has data on this, or an opinion: please share it with me and the other readers of this blog!

PS: I tried to find a picture on the internet to show 'whispering'. In all pictures, people whisper directly into someone's ear. Sometimes, they cover their mouth with their hand to reduce visibility. That is NOT what I mean when I use the word 'whispering'! For me, whispering includes full visibility of the face of the speaker!