Sub-1.0 warheads will be needed to keep current interception rates, and WH1 AMMs will be more of a dual-purpose weapon much like 10cm laser turrets are currently.
This is really a high hope, the sub-1 warheads do not save much space to begin with. AMMs will become the toy of the riches as the cost of the AMMs needed to shoot down an ASM will be (far) more than the cost of said ASM.
I dunno, I mean, just using some Java tool that somebody came up with...
It would seem that against size 6 missiles, even with low warhead strength per MSP, one can get 3 warheads, plus the 0.1 MSP "tax" and be actually more effective on paper, before decoys/ecm/jamming/etc. are factored in. And it would seem there becomes a fairly nice "balancing act" on larger ASM's because making them larger makes AMM's less effective, but makes PD more effective versus the current baseline of a size 6 ASM.
Forget anything the current missile optimizer tells you, as agility is gone

Now the name of the game is, how fast defending AMMs can go compared to incoming ASMs
Without agility, ASMs need to be faster than the current ones to make up for the hit chance, which makes AMMs' life even harder without agility.
I'll put my simple examples here, from another post:
Since the MR is fixed, higher missile speed means higher accuracy, and the accuracy is now only a function of missile speed and target speed (let's exclude E-war for now).
Speed = EP/HS*1000 km/s = (engine power per HS) * (engine HS) * (engine power multiplier) / HS * 1000 km/s = (engine power per HS) * (engine power multiplier) * (engine HS) / HS * 1000 km/s
Let's use E to denote (engine power per HS), and use some rule of thumb (engine HS)/HS values, to see how well the new missile model performs.
- For a slow beam warship, let's assume it uses 1.2x engine power, 40% engine ratio, then its speed is 480E km/s (1.2*0.4*1000)
- For a fast beam warship, assume it uses 1.5x engine power, 50% engine ratio, then its speed is 750E km/s (1.5*0.5*1000)
- For a fighter, assume it uses 3x engine power, 50% engine ratio, then its speed is 1500E km/s
- For an ASM, assume it uses 6x engine power, 60% engine ratio, then its speed is 3600E km/s
- For an AMM, assume it uses 6x engine power, 90% engine ratio, then its speed is 5400E km/s.
Then when MR is fixed to 10, we have:
- The ASM has a 3600/480E*10%=75% chance of hitting the slow beam ship, 48% chance of hitting the fast beam ship, 24% chance of hitting the fighter.
- The AMM has a 112.5% chance of hitting the slow beam ship, 72% chance of hitting the fast beam ship, 36% chance of hitting the fighter. Likely the AMM won't do any damage to these ships anyway. The AMM has a 15% chance of hitting the ASM. When it does hit, it is likely to have a less than 100% chance of destroying the ASM due to having to use a smaller warhead.
And this relationship won't change much as tech level progresses. Yes, missiles can use smaller warheads to achieve the same damage, but the reduction is relatively small compared to the engine ratio used in the examples. And when we consider E-war, such saved MSP should probably be devoted to E-war components.
Now, this hit chance is based on a 90% engine ratio AMM, which means 0.1MSP left for an S1 AMM. There is no space for the luxury of multiple warheads, or ECCM components.
If the ECCM is still 0.25MSP, that means realistically they can only be installed on S4 AMMs if you intend to keep a 90% engine ratio (leaving 0.15MSP for warhead and fuel). If multiple warheads are desired, we are looking at S5 and up AMMs.
And when the ECCM on AMMs is on-par with the missile decoy tech, the AMMs still take a penalty on hit chance based on the number of decoys.
So, things are looking pretty bad for AMMs on paper. Hope Steve's playtest prove me wrong.