You can hang the sunblaster from a fixed top or hang it from a wire. It won't sit flush on a tank top though because the bulb sticks out below the fixture a bit.
https://www.amazon.com/Sunblaster-904296-NanoTech-Fixture-Reflector/dp/B00AKKUBDQ/
At 19'' tall it's a toss up. I'd probably mount it on top of the tank and built the basking site a bit higher if you can. Within about 12'' of the bulb which will give 7'' of climbing space. If you're shining the light through a fine mesh top you'll want the light to be about 10'' from the basking spot to help make up for what the mesh intercepts.
If you want a lay flat fixture you could go with a ReptiSun hood and just replace the 5.0 bulb that comes with it. A ReptiSun 10 or Arcadia 12% 22'' T5 will fit that fixture.
You could also go with one of the fixtures from light your reptiles. They come with a great Arcadia 12% bulb and will sit flush or can be hung from a ceiling easily.
http://www.lightyourreptiles.com/22-t-5-ho-fixture-high-output-with-arcadia-d3-12-ho-bulb/