Over -4.00 diopter my left eye needs stronger correction to see with the same acuity as the right, but that changes below -3.75. Does keep eyes on the same focal plane mean make sure that your eyes are both seeing (for example) 20/30 (unless you are trying to equalize)?
Keep both eyes with the same distance to blur with correction. There’s obviously going to be a minor difference, because lenses only come to the nearest quarter diopter, but get them close as you can. If one eye can focus easily, and the other can not, the eye that can not focus can become lazy, and you’d need to patch for a few minutes a day to prevent that.
Thanks for clarifying. I’m using Snellen chart for distance to blur for Norm glasses and contact lenses and Jake’s centimetre calculation tool For Diff glasses