When I push the needle down to make the stitch, I try to have the needle at a 90 degree angle with the quilt - so the needle is going straight down. That helps make the stitches on the back the same length as the front. If it goes in at an angle then the back stitches are smaller.
I'm happy if the back stitches look nice, without too many that are too long or too short, and the top ones are even. It's a bonus if the back and front are the same size!
Janet