Part of the problem here is looking at what precisely is going on in a 20 minute turn depending on the rule set in question.
A) is a single laser firing continuously for 20 minutes such that statistically, only ONE shot is likely to hit with the rest missing?
B) is it really only one shot per 20 minutes such that only one hits if it hits, and it misses otherwise?
If A is the case, what is the difference between splitting your shots such that 10 minutes is spent firing offensively while 10 minutes is spent firing defensively? Can a gunner fire 1 shot of sand per minute - and if so, is he firing just one canister or is he firing 20 canisters and laying a field? If the latter, then he can program his "holes" such that he can take the shots when he wants to, but thereafter suffers the same penalty firing at the enemy ship as the enemy ships has firing at him. Why? Even if he programs "holes" in his screen so he can fire back - if the ship he's in even "jinks" one minute in a given direction as a "dodge" against being hit, the gunner who took the initial shot and layed his "screen" will no longer have the optimal firing solution any more.
So - which is it? One shot, one action, or multiple actions over a span of 10 minutes? Answer that question and you've got a whole new can of worms to digest. For example - if it is a series of 20 shots with only one in 20 likely to hit - what happens when you get a critical hit? Does that mean that more than one shot went home? What if a person decides to spend a 50/50 mix in defensive fires versus offensive fires? Would he suffer a -1 code in weapon offensive punch? Would he suffer a -2 to hit on 2d6? What are the modifiers involved in say, a 30/70 split for offensive/defensive fires? As they say, the can of worms just got bigger
Ultimately, if I were to try to second guess the game designers, I'd go back to STRIKER rules and see what they did there and work it from there. Note too, that I've been using GURPS rules (another heretic *gasp*) for my traveller campaigns - and they use the rules that for every shot you take, you inflict one hit for every 2 points you made your skill roll by. Thus, rolling against a 14 on 3d6 with a roll of a 10, results in 2 hits scoring a hit, or 3 hits if you roll a 9. I've also built "point defense" lasers that are special purpose built using GURPS rules where the ship can defend itself against marauders in space (and do a bang good job of stopping incoming missiles!) and be kept from actively becoming an ethics challenged trader (after all, you can't do much SHIPBOARD damage with low power but multiple hitting point defense lasers).
One reason I like the GURPS combat system is that GURPS permits the GM to use what amounts to heavy lasers instead of standard lasers. That is like allowing merchants to arm themselves with 30mm cannons, but REAL warships can arm themselves with 120mm cannons
The thing about heavier lasers in GURPS is that for the same space as 3 regular lasers, one heavier laser has twice the range as the lesser lasers, and acts in the "ye olde days of wooden ships and iron men" as 32 lbr cannons versus the civilian version of 8 lbr cannons. Imagine how a traveller universe might be if by law, Shipboard lasers for civilian use have to be of one vararity while military grade weapons outrange the civilians in a big way? All the more reasons why Ships heave to when a naval vessel puts a shot across their bows (so to speak). Ah well - time to call it quits here...
