Equalizer If that is correct it will make large beams merged by chaining absurdly powerful since all beams are additive.
EDIT: I think the concern with the problem equalizer described is mostly that it encourages ships to be built around a single giant ion beam buried deep behind armor, and makes that strategy much stronger than using prisms in any other way. IMO burying a single giant ion beam isn't very interesting, either to design, fight with, or fight against.
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Maybe one option is to change the ion combination formula to ignore number of prisms, so that efficiency is purely based on the damage being combined (regardless of how it was combined). The disadvantage of this is that it incentivizes players to always use the fewest prisms possible to cut costs, though since prisms are fairly cheap this might not be a big deal. There are already lots of reasons to use more prisms, such as redundancy and firing arc.
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Another option might be to increase the cost (figuratively) of using a large number of prisms. Making prisms expensive is a literal way to increase the cost, but that also hurts other uses of prisms.
Cost could be increased by having a very large no-build zone around the prism, similar to how weapons have a no-build zone in the direction they shoot. This means that if you wanted to bury a massive merged ion beam deep inside your ship, it would take up a lot of space because of all the prisms you'd need for merging.
Cost could also be increased by giving prisms high activation lag time, similarly to how they take a moment to power down when turned off. This would mean that adding a whole bunch of prisms means your ion beam will take a long time to "warm up", but using fewer prisms would let you be much more agile at shooting (in return for less damage/more cost). Of course, many players design ion modules to fire indefinitely, so they could just autofire to get around this.
Increasing prism explosiveness would also increase the cost. But the overall concern is that players will build ships around a single large ion prism/beam, in which case losing the main prism effectively wipes out the whole ship regardless of explosiveness.
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Regardless, it might be a good idea to make burying ion prisms deep within a ship less powerful. Perhaps larger ion beams also have a wider physical width? If you bury a giant beam deep behind armor, you'd need a very large opening to let the whole beam fit out. Though to do this the ion prism would need to be bigger than 2x2, since a 3-wide or 4-wide beam would look pretty strange coming out of a 2x2 prism.
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Unrelated to prism combining - I think it makes sense for combined ion beams to also have increased range like the railgun. Not for balance reasons, but it's generally expected for big/heavy weapons to have long range. Since the ion beam can theoretically get very big, I think range needs to be able to scale somewhat as well to help it feel good.
(related: perhaps the railgun range cap should be removed? it feels like a ship with a 500 long railgun should have at least 500 range. They're big and heavy so not much risk of kiting imo)
And one final thing - from a "feel" perspective I personally dislike prisms needing to slowly rotate to face their target. Similar weapons I've seen in other games (e.g. a tesla tower turret) tend to be fixed and radially symmetrical, with beams shooting out in whatever direction they need to without any moving parts. Obviously not a big deal though, and probably subjective.
