I often read that Boggs held an important position in District 13, and I know that in the film he was promoted to the rank of Colonel.
However, my impression of him is that he played an intermediate role in the power hierarchy.
This is partly because he is described as "Coin's right-hand lackey" and Katniss thinks of him as "a muscular robot that does Coin's bidding".
While obeying orders is fundamental to a soldier's duty, a colonel is not someone who passively takes orders. It is a role of high responsibility, to the point that in real life they are expected to command large units (regiments consisting of approximately one to several thousand people, not a dozen or a squad), take personal accountability and translate strategy into action. If the author wanted to depict the evolution of an important officer who goes from being a yes man to actively challenging a flawed leader (just like when he advices Katniss to do whatever she came to do at the Capitol, kill Peeta and not to come back), she should have clarified his position from the beginning or at least have hinted to his importance more explicitly.
For example, someone might have pointed out to Katniss that she should have realised her true relevance to the cause given that a Colonel was sent directly to the field to protect her.
“Here’s as much as I know. The president doesn’t like you. She never did. It was Peeta she wanted rescued from the arena, but no one else agreed. It made matters worse when you forced her to give the other victors immunity. But even that could be overlooked in view of how well you’ve performed.”
What he tells Katniss is something that pretty much anyone could have inferred and for which no particular closeness to Coin was necessary.
In fact, Coin had said that they should have saved Peeta in front of: "Plutarch Heavensbee. His calculating assistant, Fulvia Cardew. A mishmash of district leaders. Military officials." And the threat to remove immunity from the winners was made in public.
