To WM: Having trouble keeping/finding a constant ventriloquial voice is pretty typical.  And that's why you need what the Maher Course calls a "benchmark" word or phrase. I can tell you that I used the word "shay" as a starting point for voice placement. I learned to easily say it consistently at the same tonal pitch and with the same resonance. Then I would start each practice session by saying "shay, shay, shay", and then go on with sentences. All in the puppet's voice of course. It helps with voice placement, by the way, to practice with puppet/figure in hand.