What would change if opportunity attacks had more triggers?

Question

Our table plays with the optional rule to allow flanking to grant advantage on attack rolls, however, this seems to be too easy to achieve considering the way opportunity attacks are triggered.

I think it is rather strange that the only thing triggering opportunity attacks is leaving threatened space without disengaging.

I want to use the following rules/rulings because it kinda makes sense, and because I want to cut back on both enemies and NPCs running around their opponents without a care in the world in order to get flanking advantage. (Hell, the monk could run three circles.) But before implementing this I'd like to hear second opinions, or rather analyses.

My goal is to avoid wreaking total havoc at my table by accidentally destroying a totally valid combat tactic, or even a combat style a player might want to design his charater around after all. If someone sees that coming I'd rather not change anything at all than worsen our gaming event with a ruling that made sense only to me.

I want make the following actions trigger opportunity attacks:

1. Being prone and standing up within reach of an enemy.

The second change is a bit more complicated: We are using a grid. Moving diagonally counts as 1.5 squares movement.

2. Running through space controlled/threatened by an enemy.

   1. Moving one square does nothing (like entering your quarry's reach, or starting your turn in reach, but only moving one square within reach)
   2. Moving two squares provokes an AOO with disadvantage
   3. Moving three squares provokes a normal AOO (moving around a medium sized creature)
   4. Moving four squares provokes an AOO with advantage (this only happens when you literally run past your foe and totally ignore him)

(I'm not yet sure how this would interact with creatures or weapons with reach.)

My reasoning

Put simply: Considering the advantage that flanking gives to an attacker I think it highly unlikely that any opponent would behave like a random tree or boulder when their enemy runs past their blade to get into a better position. I don't mind good positioning, but the victims of such tactics should be bigger obstacles than they are right now. Needless to say that goes for both PCs and NPCs.

The other new trigger for standing from prone is a bit simpler: First of all standing up doesn't leave you a lot of chances to protect yourself effectively so if you stand up next to someone out to kill you should provoke a reaction. Secondly I think the status "prone" should be a great disadvantage, which it barely is. For example you could go to zero HP, drop unconscious, get healed, stand up next to the guy who knocked you down and proceed with the slaughter like nothing happened. (Unless I missed something in the RAW of course.)

An Example

To clarify my intentions, an example:

The Os are two Orcs, the .s are unoccupied spaces. 1–3 are Players Characters.

  2 . 1 . 3        2 . . . 3        . . . . .
  . . . . .        . . . . .        2 . . . 3  
  . O . O .        . O . O .        . O . O .  
  . . . . .        . . 1 . .        . . 1 . .

   fig. 1           fig. 2           fig. 3

1. Players 1, 2 and 3 stand in front of two very menacing orcs who stand just about a square apart.

2. Player 1 runs right down the middle, past both of them. He stops between and behind them, but still within their reach. So they get no AOO and have to helplessly let this happen.

3. Players 2 and 3 happily move in, flanking their respective orc with player 1 and proceed to bash their skulls in with advantage on their attack, thanks to player 1s bold and risk-free movement.

That example is the most extreme case I can think of.