I think that’s part of the Cruz strategy — he’s everybody’s second choice. As the field winnows, that will boost his numbers. (At least, that’s the strategy.)
He’s also the one Republican candidate in a recent poll who can beat Trump head to head (precisely because he’s everybody’s second choice. Take their candidate out and they go to Cruz.)
I think you’re exactly right. There will be a great winnowing of candidates after Iowa. If Cruz wins and picks up the lion’s share of second choice voters he will have the momentum.