It would seem appropriate that the different tiers of loaders have different electricity.

the arms all increase in power cost as their performance increases, and it would make sense to scale this similarly.
though i don't know if the current ones should increase or decrease to suit that.

edit: is the power usage is actually calculated based on belt speed, and therefore this is a moot question?

The energy cost does scale so to speak. The energy cost is per item moved, not a flat cost. At idle the all coat the same base amount, but start using more energy when moving items. This faster loaders have a higher max cost.

Do you think an express loader should use more energy to move 10 items than a fast loader does? Thinking about it now, I could argue that the energy per item should decrease as the tiers go up to gain economies of scale.

since it already works on item moved, it already does it use more energy, in which case i wouldn't increase the energy cost.
basically, it sounds like this isn't an issue as it already has a cost - it's linked to the belt speed based on items moved, and just not easily expressible in the UI i guess.

my question mainly came about from the listed electricity cost in the UI. i was trying AAI Loaders with a mod to make them run on electricity, and it did list different max power requirements. though the mod also said that the listed cost was not accurate.

I can't say I've looked at the accuracy of the UI display that closely, but I did notice a bit of an anomaly after a recent Factorio update that I need to look a litter deeper into.

I also haven't looked at the other mod you're referring to, so I'm not sure how that applies electricity use. I assume it is using the same in-built functionality I am.