In rereading your own email is it the delivery/wording that you struggle with, as opposed to expressing your needs?

At any point do you use the expression, "You do this...."

"I feel this when that happens. I believe xyz might be a solution. What say you?" is one example of a few in ways to assert without coming accross accusatory. Not saying that you did. But asking since it left you feeling unsettled. No sense walking on eggshells to appease/enable, yet, there's means of communication that work.