Personal Hero XP Gain

[Hades]

Do we know how exactly Personal XP Gain on a hero works? Like, selecting them to be my main game hero? Does it automatically add that extra XP into their pool, or do I just have extra XP to spend as I please added into the overall XP resource pool?

[Jerry]

The experience of the active hero increases (or to put it in other words, the experience required to the next level goes down).

[Laserstormelpies]

As of right now the best way to observe it is the following:
Get the new Hero Exp related upgrades from the elixir tree to increase the output to a noticeable amount, go to main game and turn the energy on, go to the conquest hero selection menu and repeatedly click on your selected hero to see their current Exp cost to next level go down bit by bit.
Note: should you select a hero that has the current max level for your training grounds level, then the Exp will just go into your currently available to spend Exp pool.