well, I can put the APAR guidance per face in separate light too. I am not certain of this, but all who know exactly what the APAR can cannot talk about it on the internet, so it is the question how certain any sources can be. anyways....
the dutch LCF has an 40 cell VLS, and the design allows for 48 cells. this means 5 Mk 41 blocks, or maybe 6. an VLS block can only launch one missile at the time, 1 missile per second. this means any ship can shoot itself dry in 8 seconds if required (not counting quadpacked missiles), as all VLS blocks can theoretically fire at the same time. I say theoretically, because this is just not done, no guidance system can keep track of so many missiles at once anyways, and the missiles might interfere with each other.
so let's say the APAR has 15 ESSM missiles in the air. and these are fired one second from each other, to stop interference. an ESSM goes roughly 2700 knots, and has an range of 27 nm. this means it is at it's most far away target in 1/100 hour, or 36 seconds.
so as maximum possible for the Mk 41, the system can have 32 missiles in the air of the ESSM type. or 16 if you work with 2 second intervals.
SM-2MR has an slightly lower speed but in general, more then twice the range. still, due to the midcourse autopilot of which the APAR can set an aditional 16, you can, with the 2 second intervals, still have the same number of guidance channels required.
so, here we have why it makes sense to me why the computer space would be the limiting factor for these 16 + 16: there is simply no need for more. yes, if you fire faster then 1 second intervals, and shoot the ship dry in minutes if not seconds, the APAR might come short. but APAR is not AEGIS, APAR is smaller and cheaper for an reason! it is an system that is just as capable as AEGIS, but it serves an slightly different role. so if it is never required to have more, why would they enable the systems to do so?
rumored is also that the APAR facet, which has it's square panel with round midsection, is not entirely filled with the panels, and only the round midsection is actually part of the current radar, the rest is growth space. I have not yet seen official refs for this, but it might just be......
as for who I am, I am an shipbuilding student who focusses on the naval shipbuilding. I do not claim to know about exact ship missions or systems. what I do know is what is being build, and how these vessels are build, and which is not used. an small library of books about naval architecture, design processes and other reference works, and an knowledge build up by listening to the people out here makes up the knowledge I give my comments from
doesn't mean I am always right, I'd hate it if I would be, but it makes that I always ask for proof when somebody thinks I am wrong, so I can learn more
(as the above post is mostly an thought experiment, unproven by any evidence, please shoot some holes in it if possible)