How to overlay an image over video in percent
Use

for 10% space from right, and 3% from top,

"[0:v][1:v] overlay=x='0.90*W-w':y='0.03*H'"


for 10 px from right, and 5 px from top,

"[0:v][1:v] overlay=x='W-10-w':y='5'"