In the search for a mid-drive motor kit I've found that most distributors neglect to state the size of the crank arm. The few that do have chosen a size that's optimum for people 5'9" or taller.
The average US woman is 5'4", and the average Asian man is 5'7". These groups are being discriminated against in the market of DiY mid-drive motor kits.
It's a one-size fits ~20% of the population scenario, roughly, and only one size is offered. Some kits are standard enough that it's possible to buy a separate aftermarket crankset, but the specs are undocumented and this also entails spending $100+ more and then wasting the stock cranks after spending upwards of $500 on the kit. The industry needs to get its shit together.
The product information available is lousy all around. If anyone finds data for any of the above question marks, please post and I'll update the table. These are the ideal crank specs (neglecting special circumstances like crouched over racing positions):