MLB.com writer Jim Callis got into the Mangum case in his piece today:
https://www.mlb.com/news/inbox...aft-padres-campusano
"Since the Draft, I've gotten a lot of questions wondering why seniors often sign for $10,000 or less in the first 10 rounds. Many of you were incredulous when the Mets signed Mississippi State outfielder Jake Mangum, the Southeastern Conference's all-time hits leader, for $20,000 in the fourth round.
"College seniors with no eligibility have zero leverage. The very best of them can earn six-figure bonuses -- North Carolina State first baseman Evan Edwards got $122,500 from the Marlins in the fourth round and Rice left-hander Evan Kravetz landed $112,500 from the Reds in the fifth -- but they're the exceptions. If they want to play professional baseball, most of them have to accept a minimal bonus.
"Despite a stellar college career, Mangum got dinged for being 23 years old, which is ancient by baseball standards for someone entering pro ball. He was Draft-eligible in both 2017 and 2018 and could have received a six-figure bonus in either year if he had been willing to sign where teams valued him.
"This is a matter of supply and demand rather than seniors getting penalized. That said, there is a change I would like to see that would reduce the number of seniors who get pushed into the top 10 rounds to save money against the bonus pools.
Under the current rules, if any player doesn't sign in the first 10 rounds, his team loses the value of his pick from its pool. But unsigned players from the fourth round or higher don't yield compensation choices in the following Draft, so I'd give each club the same amount of money ($2 million) for the fourth through 10th rounds and they'd get to use all of it even if some of those selections didn't sign. That would lessen the need to take cheap college seniors to push the savings to other players"