You are on to something...if a preferred holder converts while the PPS is in the basement it is so they can have more common shares than if they converted at a higher PPS.
Why would they want more common shares down the road...cause they know the price is going up.
All must remember, the preferred holders are on the inside, they have the clearest view of what's going on and what is going to happen / is likely to happen of anyone invested in this company.
And, as an inside long holder of preferreds, why on earth would they do anything to jeopardize their investment.