Me myself I tend to use full flaps for C172 x-wind unless the crosswind is stiff. I don't think the flap setting would have had much influence on the 6 kts x-wind landing the OP asked for advice about. Simply, x-wind requires that you are current in the technique, something that is quickly lost with too long time on the ground. So just keeping practicing and it will get back to you.
I remember one particular instance though when the crosswind was right at, or even above, the demonstrated. I was using F30 and did feel I was running out rudder authority during the late part of the flare. Perhaps taken by a sudden gust, but felt like I couldn't push the nose fully aligned. Since then I use lesser flap settings when it's a good breeze across.
To each their own…