Astra creating a 768 image

Been doing some test and I see that Astra creates an extra image to what WP does.
This image is 768×512 if it is a landscape image BUT if it is a portrait image it creates it at 768×1152 so unlike WP it does not have a Max heigh / Max width constraint.
So this 768×1152 Astra image is almost the same size as the WP auto created one which is 1024×683.
So looks to me like mistake on Astra’s part to omit the Max constraint.
Also Why does Astra create its own 768 x512 image. I upload at 1200×800 and turned off wordpress sizes by using 00×00 in media settings for medium and large. But I still see the 768 image so it must be coming from astra.