I get this from my 8.8Ah/36V (316Wh) possibly in similar terrain on the hilly Welsh borders.
My husband, using the same bike on the same route gets less - about 18 miles at best, but I am 52kg and he is 90kg so this clearly makes a difference. Extrapolating very roughly and very approximately.... he would get about 36-40 miles from a bike with two batteries (632wh) which seems on a par to the mileage you're getting from your bike if you're a similar weight.
It sounds possibly low but there are so many factors to consider - body weight, terrain, head/tail winds, load carried - and probably even temperature.