Flying in all different types of FSO and scenerio setups under just about all types of restrictions/conditions, it basically comes down to possibility of survival than anything else. Survivability increases drastically fvrom 18k to 25k when in buffs. At 15-18k, a attacker has less of a problem doing multiple dive attacks with a follow through for multiple tries.... versus being attacked at let's say 25k. An attacker may get one or possibly 2 fly through shots, at that alt it takes time and greater mangement of E state to keep up the constant pressure.
Add in an escort that can make an attacker deviate just 1-2k in alt to avoid being shot down and it makes getting back to advantage in relations to the bomber flight a long process. Not leaning one way or the other, but it isn't hard in some scenerios to calculate that getting back the buff group awards more than massive target annilation.
Again, no problem with it, just giving another insight into a question pondered.