CR, EL and exp? I dont get it!

[Zombimode]

Ok, Im new at GMing D&D 3.5 (I a veteran in GMing itself, just doing it for D&D 3.5 is new to me).

I recently found out that caculating exp is somewhat of a mystery to me. Specificly the role EL and CR play for it.
The source of my confusion: this (http://www.penpaperpixel.org/tools/d20encountercalculator.htm) Encounter Calculator. It gives me wildly different exp counts for encounter of the same EL, but different CRs.
Even more confusing, I get encounter that give more exp than others of higher EL.

How and why?

[Kefkafreak]

The experience the player characters gain depends on the individual CRs of the monsters / traps / whatever involved in the encounter. EL means nothing, it's just there so you know how hard the encounter will be.

(At least for this calculator)

[deuxhero]

^CR is the Rating of the Challenge an eno****er poses, hence why.

[Greenish]

It seems that a few higher CR monsters give more XP than a larger number of lower CR monsters, even with the same EL. I don't know why.

[Edit]:
^CR is the Rating of the Challenge an eno****er poses, hence why.Challenge rating is how hard an individual monster is. Encounters have EL, not CR.

[Zombimode]

The experience the player characters gain depends on the individual CRs of the monsters / traps / whatever involved in the encounter. EL means nothing, it's just there so you know how hard the encounter will be.

Yeah, thats what I dont understand.
If EL is a measure of the challange of an encounter and Exp is the reward for overcoming challanges, shouldnt encounters of the same EL always be rewarded with the same amount of Exp (for the same number of PC of the same ECL of course)?

[Kefkafreak]

No, because both EL and Experience are calculated from CR, so an encounter with EL 7.21 is easier than an encounter with EL 7.99 (which is almost 8). However, both are EL 7.