Transferring Heroes - Does it Swap or Add?

I'm a little confused about transferring heroes. I have a level 67 Nexara and a level 40 Mystery Man. If I put Nexara on the left and Mystery Man on the right, will they swap experience, stones, etc? Or will the experience from the Mystery Man simply add on to Nexara? The Transfer Details in the game say "added on to another", but the English text in this game is rife with spelling/grammatical issues, so I thought I'd ask before embarking on this expensive endeavor.

They will swap levels, tiers and astral powerups. However, awakening and hero stone powerups will not transfer. Also, the lower lvl and tier hero must be on the left, or your second hero won't show up. Transferring also won't work if one hero is a lower level but higher tier than the other.