experience for spirits

[master.jimmy]

Originally Posted by Vilk

As far I know spirit experience is very complex, I haven't bookmark the post explaining some important points, what I remember is:

• The level difference with the character plays an important role so when a spirit has the same level it gains quite less xp.
• Only the first 3 spirits use bring significant xp, after it's not significant.
• The number of enemy units still present when the spirit is used has an influence on the amount of xp used.
• For spirit attack that does damages, the xp is influenced by the damages done when other use an xp base.

man i can't understand

1) so it's better i use spirit when i'm a HIGH level hero?
2) i can't understand
3) ?? if many units remains after using Spirits XP will be more or less?
4) "when other use an xp base." what does it mean?