Hi, we had a look at this. Using the "A-4KU with Mk82s" loadout example.
The "problem" is that you are instructing the aircraft to attack without the context of the flight plan. The loadout settings for throttle, altitude etc. all assume the presence of a flight plan for the strike. In your case, since the aircraft is not on a strike mission and has no flight plan, the "doctrinal" settings of the loadout are contrasted against the weapon release envelope and, since the doctrinal altitude is NOT within the envelope limits, it is ignored, and priority is instead given to making sure that the aircraft is within the weapon release envelope (which it is, since the Mk82s can indeed be released at high altitude - never mind that you'll have terrible accuracy).
(If you are surprised that the "doctrinal" altitude is ignored, consider the alternative: Plane blindly follows the doctrinal altitude all the way to the target, and does not drop the bombs because its altitude is higher or lower than the bomb release envelope. Oops.)
If you assign the plane to a strike mission against the target, and add a friendly base so that the AC plots a proper flight plan, you will see that the plane indeed descends to low altitude as it closes on the IP point, it remains there during the final ingress and strike, and egresses as appropriate.