1 pointI'm not entirely sure what it would be for the SI 24's. The cone holds a lot of volume but the surround is huge and protrudes a lot unlike the pro drivers. Also the frame is really thick on these and it'll be front mounted which moves the whole assembly forward quite a bit. It may actually be less than a back mounted 21" pro. This is probably a good generic guess. AVH...300-350cm2 for each driver should be added to S2. This is used rather than Atc/Vtc. It has a better track record, in my offset designs at least. Also the AE drivers have extremely low inductance. I doubt the complex inductance modeling will make much difference at all on them. I wouldn't worry about it. Yes the inductance modeled correctly would be slightly more accurate but it'll be a very small difference on these. These are the exception rather than the rule for bass drivers.
1 pointMy 2 skrams are mixed with 8 sealed ht18s. Sounds great to me
1 pointWhen going with the larger angle (60°) I‘d move the drivers as close together as possible, simply for the space efficiency. In that case, you could basically reduce S1 to like 500 and also substract 1000qcm from the other cross sections. Ftc and Atc are left empty in my case because that section is integrated into S2. You can try to shape the rear, similar to what Ricci did in the Othorn, but I don‘t think it‘s gonna have any real impact with the 60° angle and after moving the drivers close together. It‘s a bit annoying to manufacture those parts for sure. For the AE drivers you‘d have to find the complex inductance parameters; I think you could eventually use these from the 15“ unit Ricci measured. This is a special case, in which I‘d not fully trust HR to simulate it by itself, since these have an exceptionally low inductance (double clicking Le which turns it RED and enables semi-inductance simulation).