Good post above, so, just to add to that a lil bit...assuming there are a lot of ebike owners with a one size fits all frame, it isn't as easy as using stock measurements of 110% of your inseam.
Not IMHO
Rather a proper fitting should include a set up with your hands on the bars and an adjustment on that universal frame to marry up with the 'riding-fit', not nessessarily only the standover 'upright on saddle' fit.
A proper fitting and or saddle height depends on the angle of knee bend for optimum power efficiency; in conjunction with stem height/angle/ length etc.
Take your time, lean your bike against a wall or have a mate help keep your bike upright while you 'fit' into it.
Geometry, universal frames sizes, stem sizes and set up all play a factor in achieving optimal comfort for your eBike.
Not many ppl change the stem or adjust it accordingly and are stuck with only saddle hight, therefore never really knowing what truly feels proper for them.
I am 6'2" but have long legs for my body. My inseam (all pants I wear) are closer to 36" whereas most friends I know that are 6'2" or taller only have 34" inseams, I have one close friend that is 6'5" and we have the same inseam size. Where does that leave me then? I have no choice but to adjust seat angle back and up and shorten the stem and eliminate rise.
It's fun to fine tune but when doing saddle height, bear in mind that isn't the be and end all of 'fit'.
Happy riding everyone.