Many buckled baby carriers offer two configurations for parents comfort - rucksack (H shape) or crossed (X shape) and which is more comfortable really depends on you. Shape of your shoulders and how the straps sit across your back will all affect which you find more comfortable. Which is why I hugely recommend trying both (and you can read more about both and the differences here).
However, most manuals and most videos only show the H shape so parents often don't know how to do the cross. Or try it and its not quite right and they are not sure if they've got it quite right. So here is how to cross the straps and how to get is comfortable;
The trick is to pull the straps down first. Often parents try to catch the strap at the top near their shoulder then move it around and under their arm. Instead I recommend catching the strap low down, near your lower back or bottom and then pulling the strap straight down toward your bottom and then come across your back to plug the strap in. This can seem harder at first, but as you can see in the video it gives a much wider sweep that gives you so much more support and spreads the weight evenly across your whole back. And I am promise it gets so much easier once you've done it a few times. And if you are ever struggling to find the strap behind you try gently swinging and that strap will swing into your hand, or lean slightly forward and again this will bring the strap into your hand.
If, however, you do find it hard and instead catch the strap near the top and the cross ends up high and near your neck. Or if the straps ride up after a while... fear not its a very easy fix!
Simply loosen your straps slightly then using one hand at your shoulder and the other under your other arm, wiggle the strap wider and down (respectively) as shown then retighten as needed and voila a nice wide supportive cross!