One basking spot will work if it's large enough for a dragon to bask their entire body under completely to get an even bask. UVB should be right next to the basking light for most intense UVB along with highest temps. In very large enclosures you can sometimes add a second basking spot that is just heat with no UVB but you need enough space to provide a gradient. You still want areas with little to no UVB and daytime temps around 70-80.