Fit, crop and stretch are different
Fit preserves the aspect ratio and keeps the whole image inside your requested box. Crop & fill removes edges as needed so the output completely fills the requested dimensions. Stretch forces exact dimensions and can distort the image.
About enlarging
Increasing pixel dimensions creates a larger raster but does not reconstruct detail that was not present in the original. For best quality, start from the highest-resolution source available.
Batch behavior
Every image in a batch receives the same output settings. The result list shows the actual generated dimensions so you can verify the operation before downloading.