Is this for your basking light? If so, it really kind of depends on the temperatures you're reading in the tank. It's OK to put it on the top if you want but if you can suspend it above and adjust the height of the lamp then you can fine tune the temperatures a bit which I find to be helpful.
In that case you want to keep it pretty close. The screen will intercept some of the UVB so if you can cut it below the light it may help. I advise replacing the 13w because it's not powerful enough to be of much use. If you stick with the coil type I suggest the 26w UVB200 which will put out adequate UVB at around 6'' below the bulb. Beyond about 8'' the output really drops and it's not useful though. There are higher output options available that work very well in larger enclosures if needed.
I have a smaller tank so that should last for a bit right? I got her two days ago and she is starting to shed already so im guessing that is good. The tank is about 30 gal but she is a baby about 3 months old.
Shedding is a good sign, yes. A 13w won't work in any tank for a bearded dragon but if you swap it out for the 26w UVB200 it should work well for a little while as long as you can set it within about 6-8'' of the basking area.