I noticed that the standard errors that can be computed for say, the AE model, return the same standard errors for the A and the E estimate. Is this expected? Just want to be sure. I know SEs in general aren't recommended for CIs, but I am doing this for the sake of a different analysis so just want to be sure that this is what would be expected. I noticed this isn't the case when it's a full model (ACE, etc.).

Also, would it be fair to say, the SEs of given constrained parameters (that are constrained to 0) are 0 themselves? That's what it looks like for the cases in which you calculate the SE of C for the AE model, for example; but as an alternative example (as this isn't technically fully modelled), for example, if the ACE model C parameter is positive (in the direct variance approach), is it appropriate to say the D estimate is 0 (logically, albeit, D = -C in another line of thought), and the D SE is 0?

Thanks as always!