It is your target speed, distance, and aspect that appear near the TD box

Which is kinda irrelevant isn’t it?

Either you can lock it or you can’t, whether it is doing 40kts or 400kts, if it is within the off boresight range of your missile it will lock, if it isn’t it won’t. Otherwise what is the point of high launch manouverability and high rate of turn seeker elements and wider FOVs?