To understand the modifier mechanic for the standard turbolaser (we'll call it STL), you first simply have to understand how each individual modifier would affect it statistically. Primary attributes (realistically) are strength, range, accuracy, velocity and energy(efficiency/exchange (or simply, consumption)).
[HTL] The Heavy modifier would make things twice as damaging, but less than twice than its effective range, cost a little less than twice the consumption of two individual weapons of the same time (which wastes less energy as one process (think having one big transformer instead of several smaller ones)), have only marginally better travel velocity and likely even less-than-standard accuracy due to the increased bolt size and capacity.
[LRTL] The Long Range modifier would probably make things about two and a half to three times as far-ranged and almost that in velocity, but only twice or slightly better than in strength, with the focus being on the stability of the bolt (and strength of its field) rather than the quantity or charge of the plasma/beam. Muzzle and travel velocity would naturally step up, but not by much more than a Heavy variant, accuracy would increase in similar fashion and the cost could be said to be around two and a half times the cost. The name of the game here is stability, not potency, and like a sniper rifle, these weapons would be made for their effective range and ability to retain damage, rather then deal it immensely and outright like an AK-47, for example.
[H-LRTL] Mixing the Heavy and Long Range modifiers together yields some interesting results, as one is not only stepping up the range, accuracy and velocity, but also the raw damage potential via size. These weapons would be massive in comparison to their generic siblings. At this level, simply firing such a weapon might require reducing consumption from other subsystems during firing to facilitate the sudden energy demand for all but the largest of ships (as while your reactor might be able to handle it, your power lines WILL NOT, and there's no such thing as overloading a wire - you will generate tons of heat and a massive energy efficiency DROP from even trying - as in lose energy in the pipeline). Fire rate is also going to naturally sink, but predictably so. Your effective range is going to be -almost- doubled as opposed to a standalone HTL, the damage might be close to double (though probably closer to 1.5-1.6x your LRTL), and the velocities and such will also scale up roughly linearly.
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TLDR: Some aspects scale linearly, others logarythmically. It's important to note that your damage yield is always going to be gradually less efficient the larger in scale the weapon grows, but the effective range and travel velocity may scale quite sporadically depending on a number of factors which can't be charted systematically in a linear pattern. There's also ALWAYS SOME FORM OF LOSS when scaling said things up; it's never a point-for-point X-times increase, for instance. Bigger isn't better. A bar of steel isn't twice as strong just because one made it twice as large, as it's still steel. Consolidation is more efficient in energy but less efficient in potential.
Niche is the key word for these, especially when stacking multiple modifiers.
Sources: Student Electronic Engineering Technician & Weapons Technology Engineer.
