Monmouth's NH poll asked whom voters would choose if only top 4 left, & found Biden helped most
by the field narrowing.
https://www.monmouth.edu/polling-institute/documents/monmouthpoll_nh_010920.pdf/
The Monmouth poll also asked New Hampshire voters who they would back if the nomination race came down to just a few candidates by the time of the states February 11th primary. No single candidate emerges as a presumptive front-runner in a scenario involving just the four candidates who lead in the poll right now. Bidens vote share grows by 5 points to 24%, Buttigieg increases 3 points to 23%, Sanders increases 3 points to 21%, and Warren increases 3 points to 18%. Another 5% half of whom are Gabbard supporters say they will not vote for any of these candidates in a four-way race.
There appears to be no natural heir if the field winnows before New Hampshire. Supporters of lower polling candidates tend to disperse fairly evenly among the top contenders, said Murray.
Personally, I would not call that distribution "fairly even," with Biden picking up more than 60% more voters than any of his top three rivals from the less successful candidates dropping out. He picks up almost 36% of those voters, while his top 3 rivals pick up slightly more than 21% each.