similar sized provinces work best, but my kingdom does use a range which eases chaining
the difference from average maybe no more than 15% in NW (both low and high, but especially high), in terms of acreage it can be a little higher. Use a right skewed size distribution (i.e. with the modus being higher than the mean).
use the biggest province for sending aid, use the modus sized provinces for chaining and use the lower tier provinces for honor grabbing.
If you pick a kingdom that has roughly equal activity but with some T/M's, super thieves or super mages you will win 100% of the time and get a withdrawal out of them, because them losing honor due to attacks will make any kingdom withdraw because it lowers morale (acres can be gained easily, honor cannot).
You can pick your war targets about 100K, 200K, sometimes even 300 or 400K bigger than your kingdom in terms of networth, ensuring they'll be enticed to war you.
Last age my kingdom got 3 war wins, 2 counts and numerous barons using this tactic. We tied the other two wars, due to our activity being sluggish and taking on a kingdom with too many DE's (eh summer vacation always a bad age for our kingdom).