The reward given is reflected of your level as well. It's capped a certain amount, so if your level one you can't get carried through high level fates and get massive amounts.

If you match the level of the fate you and get gold, you will get the maximum amount of xp possible for that fate.

For example, level 32 fate you'll get 15k xp, if you complete that at level 30 you'll get around 13k. At 28 you'll get 11k and so on. Figures not accurate.

This is why it's not necessarily worth jumping to a high level zone quickly. You're better off staying at fates as close as to your level as long as possible, due to ease and the xp being capped.