Yes, 0 to 4 is actually five hardpoints. Nice screen shot.
The Frigates are balanced in game to be the counter to the Tartan (corvette class) so they have a larger Miss number at 70? That would be a game counter balance issue.
Distance away and size does affect hits (physics engine collision)...but that number is primary for the percentage of miss shots at a given set nominal distance. The Tartan would at distance miss 70% of its shots at a Frigate Class ship but only miss about 5% of its shots to a Fighter Class.
The Damage in the ship XML is actually only used by the AI to calculate Auto-Battle option in a given fight, and also what the AI considers the 'strength threat' of the ship.
I would make sure to change the 'real' damage done is in the Projectiles.xml, such as in the above example 'Proj_Ship_Medium_Laser_Cannon_Green' for example. Try to set THAT number to quite high and see if it does do a one_shot kill.
I hope that is the number which is changed, in Projectile.xml, not the normal ship.xml
Plus the other Major Factor you can set the "Armor Matrix" value so that the damage done to other "specific ships" is multiplied by a given number, so from Tartan 2x projectile damage verse X-Wing fighters armor to 100x.