Something to think about... early in preseason, first-teamers see little to no action. One series at most... and if this depth chart actually shows which teams the players will be lining up with for the pre-season games it sort of makes sense. Generally, all the first-teamers on that list are known quantities, and it wouldn't make much sense to the coaches to leave them in for large amounts of playing time. The second teamers however, they are mostly new guys to the team, and probably need some more playing time before the coaches know what they have in them.
To see McMichael down on the depth chart does not mean he will not see playing time come regular season. It just means for now, he will not be lining up with the first-team often in pre-season games. Once he goes out and proves himself in extended playing time a few more times we will see him move up that chart quickly. The same goes for the other surprise players that are low on the dept charts.
Anything before the third pre-season game means basically nothing. That is when the final roster will start to take shape, and you will begin to see who the starters will be and what our offensive and defensive schemes will look like, with the units playing as a team. Until then, the pre-season is all about personal performances and catching the coaches' eyes in order to get more playing time and hopefully elevated to first team.