Why is my weight-based shipping calculation incorrect?

[DrivenCornhole]

I have all the items in my store individually calculating shipping price I set correctly. I have my shipping profile set by item weight. My settings are 3.99 for 1lb and under and 5.99 1.1lb+. My tshirts for example have as weight 5oz and they come out at checkout 3.99, which is correct. However, If I add a second tshirt (10oz total) the shipping comes up at checkout as 5.99. What am I doing wrong in my settings?

[sniper2804]

Are both of your products from two different shipping profiles or two different origins by any chance?

[DrivenCornhole]

I just checked and all my active products are in a profile I created with the parameters mentioned previously.