@rsog412 Any assignment that doesn't see Bonifatius assigned to Myne's immediate proximity (and therefore make your D = 0) pretty much takes him completely out of the equation as far as the initial contact goes. If Myne's guard is strong enough to survive the initial contact long enough for reinforcements to arrive, Bonifatius' presence in those reinforcements is mostly moot, since even Bonifatius isn't going to be able to outweigh the entirety of the response that the Knight's Order can muster if one of their archducal candidates gets attacked. If on the other hand Myne's guard can't last long enough, Bonifatius' presence in the rapid response force also makes no difference, since by the time he arrives, Myne would already be dead. The only way for him to make a meaningful difference with respect to Myne's personal safety is if he's there to tilt the balance in the initial point of contact.
It is for the above reason that the balance of whether Bonifatius would be a good guard knight for Myne is solely down to whether your C > A. I'm of the position that A is something that is controllable from the Ehrenfest side, whereas they have zero control over what C can be since they cannot know with certainty what assets their enemies are prepared to commit in going after Myne, so better the devil you know than the devil you don't.
As to whether Bonifatius guarding Myne is the best use of his skills, that I argue is tangential to whether he would be a good guard knight for her. The latter being true does not require the former to also be true.