Email Format Improvements or Ability to Modify

I need the ability to modify the email format that gets sent through subscriptions. The size of the image in the email is far too small to be legible in an email window (both on phone and desktop), and prevents us from using subscriptions to fully automate our reporting. This is the biggest drawback to adoption that I face today. Execs don't like the small print or the thick Microsoft borders, which combined require them to open the attachment to read what is supposed to be a quick flash of data for them. It would be great if we had the ability to modify the format that gets sent or to at least make the general improvement to increase the image size and/or reduce the thickness of the Microsoft borders in the email. Either modification would help, but both would be great. Even better if we have the ability to modify ourselves.