According to Kindle the requirements for the size of cover art is:
• Minimum of 1000 pixels on the longest side
• Ideal height/width ratio of 1.6
For better quality, we recommend that images be 2500 pixels on the longest side.
Retrieved from https://kdp.amazon.com/self-publishi...A2J0TRG6OPX0VM
I have used an image which is 1657 x 2500 in my Sigil file. This looks massive in Sigil. Is it too big?