Generic victory point system for large games

I'm hoping to be putting together a reasonably large game in a couple of weeks, and I was pondering a victory point system. I would like it to simply reflect the custom of ships of the line not engaging smaller ships in a conflict, and I want to keep it as simple as possible. So, here's what I'm thinking:

A sunken/surrendered ship is worth it's burden in victory points to the attacker.
A ship which opens fire on an opposing ship with a burden of two less than it's own, or smaller, earns a victory point penalty equal to the difference between the burdens of the ship.
This victory point penalty is waived if the target ship has fired upon a ship of equal or greater burden than the attacking ship, or if the target ship is the highest burden ship in it's fleet.

Any thoughts on this? Does it seem reasonably straightforward? Is it workable? Do you think it will be a reasonable emulation of the element I'm looking for, accepting a certain amount of abstraction common to most mechanics of this game?

It seems like it would work fine in broad terms. If you drill down there are some spots of weirdness around the edges, mostly because the frigates span a wide range from burden 2 to 4. So a third-rate would take a penalty to shoot at HMS Concorde but not at HMS Amelia. HMS Amelia would take a penalty to shoot at Le Succes but not Hermione.

It would take someone more historically knowledgeable than me to outline how this tradition was understood by the participants, and worked in practice. But my hunch is that it would be best just to split the ships into line-of-battle ships (burden 5+) and everything else (burden 4-) and if the big guy shoots at the small guy assess a flat 2 VP penalty or something like that...

I think you overstate the effect of this "custom."

It would be more accurate to say that Line of Battle Ships generally ignored frigates and smaller when in the presence of their enemy counterparts, as those smaller sorts of ships were no threat to them. 3rd rates never hesitated to engage a frigate that acted in a hostile manner, nor, as demonstrated by July 1812 chase of the Constitution, were they above attempting to overwhelm a frigate when they had nothing better to do.

I know this is not a direct answer to the question, but I would submit that any rule that penalized ships of the line for engaging a frigate in the skirmish-style scenarios handled in sails of glory is highly ahistorical.