Tonight we had 7 more on but had an ENY of 29.
Aww... 7 sounds so little, doesn't it?
But for good reasons, ENY doesn't care for absolute numbers. But for relative ones. 7 players can be 5% more.... or 500%.
107 to 100 players won't give you any ENY. 10 to 3 players will give you ENY 29. Both times "only 7 players more"
In other words: It was a low populated arena and the smallest enemy country had either one or none defender at all.
And why should ENY refelct number of bases? Bases do not fight, vulch, horde. They are just a place to take off from, and a player can only take off from one base at a time.