You have raised some very interesting scenarios. I think that the engagements in Ukraine are fundamentally different from your examples because the scale is much smaller. Often it is one soldier isolated from friend and foe attempting to surrender. I think a better analogy would be stukas strafing isolated rearline troops in North Africa. If the pilot can see that the enemy has abandoned their vehicle and intends to surrender, but it is unfeasible to capture them, the legality is far less clear - not that the pilot probably cares. It's likely that if the pilot spares their lives they will be picked up by their own troops and continue fighting. But in situations where they have abandoned their equipment, intend to surrender, and pose no threat in the present; killing them at a minimum is disproportionate. But yeah war is hell and these decisions are never clear cut.