i like that of the original species in bionicle (ie: built by the great beings pre-launch, rather than mata nui) they get progressively larger and less interesting as we learn about them
Hydraxon's (barramoi) - Largest of the lads. 9ft or so. No powers, just a guy.
Axonn's (akiamu) - Not much taller than a glatorian really, just beefier. 7.5ft. Limited "powers" (ie: create lightning)
Toa - Glatorian size or maybe a bit smaller. 7ft. Literal demigods of their "elements" (ie: control lightning)
Matoran - Agori-size??? Smaller than an Agori? 4.5ft if i recall. Contains the power to transform into one of the aforementioned demigods
I like to see this as a sort of progression - from the clunkiest and most basic of synthetic life, utterly lacking in special abilities and completely reliant on physical size, strength, and skill to fight, to the incredibly compact Toa that's no larger than the typical glatorian warrior yet full of unimaginable power.
The great beings had to learn as they went and actively applied everything they discovered to waves of progressively tougher security with the occasional one-off experiment - god forbid some layman break in and discover all your sinister machinations