There are many techniques to taking an implant impression. There is the open tray technique and then there is the closed tray technique. And no matter which technique you prefer, it is important to make sure the impression coping or post is connected correctly to the implant. Taking a radiograph is one way to ensure the component is seated and connected correctly.
Recently as an instructor at a dental school, I noticed that on two occasions the students were not able to feel how the connection works. Both students were struggling to get the components seated. On both occasions, the implants were quite subgingival and so a visual check is not possible and that it is only by taking a radiograph can you confirm if the components are seated correctly.
In cases like that, the way I ensure that the impression coping is seated is to apply gentle downward and rotational forces while I am tightening up the screw. If the coping is fully seated, then it would be engaging the ant rotational feature of the implant, then there would be resistance and no movement when you apply downward and rotational forces. If I am not sure if the component had moved while tightening the screw, then I will gently apply rotational force to see if it can move. If it can move, then the component moved in an occlusal direction and I have to re-engage before tightening up the screw again.
I have worked with many different implant systems. Depending on the connections, some systems are easier to work with and some are harder to work with. But this has been my technique to ensure the impression coping is connected. There are of course some impression copings that do not engage the anti-rotational feature and so for those cases, this technique would not apply.