As Jorgen says, this is a minor problem on the verge of being completely irrelevant. Gauss are primarily a weapon for use against missiles, in nearly any other purpose they are nearly always inferior to another weapon type aside from some relatively rare edge cases (mainly at very low/very high tech levels).
The primary reason smaller Gauss weapons are better is due to salvo overkill effects due to the lower hit% per weapon. Basically, since a single weapon can only fire at one missile salvo per increment, any shots left for that weapon after the salvo is destroyed are wasted. Thus, having a higher volume of shots with proportionally lower per-shot accuracy leads to more efficient allocation of fire. This has been tested empirically in the past by other forummers.
The advantage to larger Gauss now in 1.13+ is fire controls, as a single-weapon fire control can be used to control only one Gauss turret you would want the single turret you put on your ship (or two if you design for redundancy in all cases as a design philosophy) to be as good as possible. The tonnage savings from using one or two SW fire controls instead of MW might make up for the salvo overkill losses, especially on a smaller multi-role ship.
So... larger Gauss produce less leaking missiles as they are more consistent
I don't think this is correct, due to the law of averages/large numbers more shots at lower accuracy per shot should lead to more consistent behavior, not less.
So, the problem, I think, is that for squadron-size through fleet-size forces with usual crews and officers smaller gausses are not-significantly worse against fast missiles at average or small numbers, equally good against slightly-less-then-average missiles at nearly any numbers or average missiles at large numbers, significantly better against slightly-better-then-average missiles at more than expected numbers (a shift from nearly 0% chances of not being at least mission kill towards some positive chance to withstand fire), and, finally, drastically better against slowish missiles at any numbers.
Similarly this is incorrect for the same reasons. Gauss of
any size would have the same theoretical efficiency given the same total volume of weapons (number of shots * accuracy remains a constant value), and larger Gauss are more likely to suffer from overkill effects leading to greater volume of wasted shots.
There is some chance that a larger Gauss weapon is more likely to defend completely against a small salvo which would otherwise leak, but this is due to the
inconsistency of large Gauss fire, and there is an equivalent chance for missing significantly more shots and taking extra damage from missiles. Regardless, large Gauss do not provide better performance in any case given equivalent configurations (volume * accuracy).