well I do not proactively hit t10 kingdoms but hit them most of the times they hit someone in my kingdom, be it myself or someone else, it does not matter if I hit the original hitter as long as it goes towards the same kingdom, occasionally I do randoms too, but find most of my growth doing retals.

stats looks like this and about to hit 3500 acres without spending more than 1 hour or less logged in a day, probably more like half an hour on average

Total Attacks Made 35
Total Wins 31 excluded some ambushes, not sure I failed a hit, but if so only one
Wins Against Larger Opponents 11
Average Relative Opponent Networth 99%
Total Land Gained in Combat 5875 explored to arround 1100 acres so 189 acre a hit on average from there if going by 31 sucesfull attacks
Attacks Suffered 29
Times Defeated 26 I think this is without one hit that was conquests and two ambushes
Total Land Lost in Combat 3812 this is 147 acres on average for defeats, not sure if ambushed acres are counted, if so the average is less per sucesfull hit