I've never really been satisfied with the way the official Star Wars D6 handles differences in scales when it comes to damage. In the First Edition rules, it was stated (roughly) that the listed damage of vehicle weapons would be doubled if used against a character-scale target. Thus, a 6D Quad Laser cannon would do 12D versus a humanoid target. This worked well enough—until you got to the reverse: a TIE Fighter with a 2D hull could rather easily be heavily damaged/destroyed by just 2 or 3 shots from a standard blaster rifle (which would do about 2D+2 damage in vehicle scale). Now, I know TIE fighters are supposed to suck, but.. not THAT much.
In the First Edition 'Rules Companion', the whole idea of 'die caps' were added. For example, a person using a 4D Damage blaster pistol against a landspeeder with a 2D Hull; If the attack hit, 4D were still rolled, but the 'cap' on the die was 3. Thus, anything OVER a 3 became a three. Instead of a max damage of 24, you'd have a max damage of 12. I didn't particularly like this- for one thing because there were a LOT of different scales. Character, Speeder, Fighter, Walker, Capital, etc., so you really had to use a chart to figure things out. Also, mathematically, the rolls for 'capped' weapons were skewed to always roll towards the upper end of their range: for instance, with a cap of three, if you rolled a 1, it counted as a 1; a two, it counted as a two, but if you rolled a 3, 4, 5 or 6, it counted as a three.
In all honesty, I don't even remember what 2nd Edition used to solve these scaling problems, because I had already kind-of worked out my own system by that time. I have been refining it ever since and pretty much now I use a very simple (in my opinion) way to handle damage between targets of different scales.
There are three scales in my system:
Character (things the general size of a human)
Vehicle (things from speeder-bike size to light freighters)
Capital (things from medium freighter size to star destroyers)
Theoretically, there is a 'gargantuan' size category, for things like the Death Star, but I can't recall a single time where I ever needed it in my own campaign.
Damage between scales is simple:
For every scale you go up from character-scale, the number of dice is divided by three
A heavy blaster rifle does
6D character scale damage
2D vehicle scale damage
0D+2 capital scale damage
An E-Web 'blaster cannon' does
9D character scale damage
3D vehicle scale damage
1D capital scale damage
A quad-laser cannon does
18D character scale damage
6D vehicle scale damage
2D capital scale damage
A turbolaser does
36D character scale damage
12D vehicle scale damage
4D capital scale damage
Of course, this means I've had to adjust the hull ratings of some of the vehicle slightly lower (for instance, the X-wing now has a 3D rather than a 4D hull, because... seriously, 4D was just a bit too much).
Again, I like this because there is some symmetry to it. For instance:
An 'average' human has a 2D strength and the average blaster pistol does 4D;
An 'average' starfighter has a 2D hull and the average laser pistol does 4D
Now, keep in mind there ARE different modifiers for HITTING things of different scales/sizes, this system only covers damage taken when something is hit. And obviously, if you're a player character, no matter how strong you are, you do NOT want to get hit with a turbolaser.