KeyPOST is essentially agnostic, it doesn't care, about how the sign structure components are fixed to each other. We don't model the clips for example. The most important thing for a foundation is how it interacts with the ground, and we assume all of the wind forces transfer down to the ground. You could, I suppose, have a socket or other fixing type that dampened and potentially reduced these forces, but KeyPOST would still assume the worst case.
So, normally you can just design your sign structures in KeyPOST and then specify the socket installation to your site team. However, I understand that much of the time sockets are used is to provide reusability if the post is damaged. This usually requires greater embedment, to eliminate the chances of the foundation breaking, and/or also by adding rebar. Minimum embedment would seem more prone to failure than additional volume or strengthening. But this would all be, from a structural perspective, above and beyond the structural and geotechnical requirements.
We have had conversations with suppliers but not arrived at a suitable number for additional embedment to strengthen the concrete, when sockets are used. Rebar is so rarely used for traffic signs, specifying it is not something KeyPOST can do at the moment.
In summary, KeyPOST will still give correct calculations whether the post is directly embedded in the concrete or in a sleeve/socket. You may get some figures from the suppliers of sockets, and I believe some at least have done real world, crash testing. If you can find a number, you can adjust your designs in KeyPOST accordingly, by specifying the dimensions of the foundation you need, which will be larger than KeyPOST says is needed, and it will recalculate the outputs based on your inputted dimensions.