A: If your baby has reflux, he may prefer sleeping in a more upright position. However, I suspect that it may not actually be the horizontal position that he prefers; he may just prefer being held.
A good first step: put him down while he's awake for his bedtime routine and feed him; this ensures that his final nighttime feeding is at the start and not at the end of the routine. Once he is in his crib, sit next to him and pat him to sleep. He may not like the change at first, but after just a few nights, he’ll get the hang of falling asleep without being held. Once he starts to fall asleep in his crib, start gradually moving yourself farther away until he is completely soothing himself to sleep.
It can be a difficult process, but it will likely help your little guy learn how to fall asleep on his own rather than needing you to hold him to sleep, especially if he also wakes throughout the night and has to held to fall asleep again. Persistence and consistency are the key to making these changes, but it will help everyone get the sleep they need!