I'm sorry but I don't agree with that chart. If you look at the distance recommendations for the standard Repti-Sun 10.0 tube, it shows 10 to 18". With the testing that Frances Baines (the UVB guru) did, her results showed that in order to get the full benefit of that particular bulb, the distance should be 6 to 8" from the beardies while in their basking spot.
On your chart, it shows the distance of the 10.0 HO bulb should be within 18 to 36" and I don't feel that is sufficient. Do you have a Solar Meter so you can get a reading of the UV exposure at the 21" distance?
With the Arcadia HO 12% bulbs, a 12" or just slightly more is recommended.
I just want to make sure that your little beardie is getting sufficient exposure like he needs.