The way conquest rewards are structured is the lower tier chests actually have more gear less shards (zetas I can't remember) and the high tiers have less gear and more shards. The rationale for it is, if you are getting lower crates, it means you need to develop your roster more. So they give you more gear to build your roster. That way you can achieve high tier crates next time.
If you saw 5 zetas in the 3rd chest and you got 3 zetas in say 4th or whatever higher chest you got. It shows zetas also follow this logic. It has always been this way, and as far as I know, it has never changed.
Next conquest you can check yourself and see how they change over the different tiers.
It seems backwards, but there actually is method to the madness.