orang3eph

Look at it this way
90% Confidence = 10 % Alpha = 1.65 reliability
99% Confidence = 1% Alpha = 2.58 reliability
Using the same methods as I mentioned above, see how the formula reacts.
If Alpha (Level of Sig) decreases, your reliability level is higher… Therefore, your interval is larger. Which also makes sense…
I dont see the contrary
X = 10
Standard error = 5
@ 95%
10 + 1.65 * 5
10  1.65 * 5
@ 99%
10 + 2.58 *5
10  2.58*5

you can see at 99% (1 level of significance), the interval is larger.