My Viv is 18" high and the UV tube is at the front/top. But I have a raised basking area to allow the beardie to be closer to the UV. I'm happy with that and the Beardie seems to be. He's doing everything he should be doing, eating, poo-ing and sloughing with ease, so I've no concerns.
I have seen Vivs with the UV tubes slung low, to place them closer to 'ground level' but I opted for the above arrangement so the tube was hidden from view.
If you're worried it may be an idea to check with your rep's breeder.