There is an ngon in this topology. For this particular issue I tried to cut in some quads; however, it is the equivalent of a max inset topology wise and will result in the area rounding when subD is applied. For my next attempt I tried cutting in control loops around, but this just repeats this problem over again in…
why don't you try sending those edges around horizontally instead of bunching them up at the top? There's no extra detail at the top, but there's a gentle curve around the side on your ref pic that could be defined later on.
The final shape is as marked in purple in the below image. This surface will be flat, so I will try just adding support edges on the corners as you suggested. Thanks
what is the final shape you wantt to achieve? NGons on flat surfaces are not a problem. from what you've posted it just looks like you need to add support geometry to keep your corners hard.