Mp4 to gif output dimensions arbitrarily different - why?

Hi - using the Creative Cloud Express free video to gif tool and don't understand why selecting same options for videos each taken on same device within minutes of each other (so no settings changed or anything - pretty much same subject, etc.) are being processed into gifs with different dimensions. For each I select square aspect ratio and fill screen, but somehow the squares are coming out in two different sizes, seemingly without reason. I thought it might be to do with file size, as a smaller size file came out as the preferred large square gif. But then one smaller than this in file size was processed as a small square gif. I just want them all the same size squares! Any ideas?

I'm using this on android phone by the way, brave browser, and seeing output gifs' dimensions when inserting into google doc. If that makes any difference