We (my friends and me) are not sure about the climb rule. In AoS you can climb an obstable, so you can be in the middle of a wall, for example. Another rule says flyers ignore vertical distances when moving.
Nagash is at 9" from those 5 Clan Rats at 9" and there is a wall between them. If Nagash charge with a 9 (6+3), can he attack the Clan Rats? The base doesn't fit between the wall and the rats and he has not enought movement to flank and attack by the side where he has enough room. I can