I'm using a rappel extension similar to what is shown in this video and that one. When the rappel start is a straight drop-off from a ledge and the anchor is low to the ground, I find it difficult to start the rappel as shown in FotH 9th ed. p.216 (description below) as my ATC (tube-type breaking device) often gets stuck above while I lower into position below the ledge and weigh the rope. An obvious solution to this would be to forego the extended rappel and clip the ATC directly to the belay loop and clip the autoblock on the leg loop but I'm not a big fan of the leg-loop approach. Is there a way to start straight drop-off rappels using an extension without getting my gear stuck above?
As to the technique described in FotH:
Essentially the procedure it describes for steep ledges and/or low anchors is to 1- sit down on the ledge as though sitting in a chair; 2- start to rotate to your left until you're facing the rock (assumes right hand is brake hand). This works much better when you can find decent footing. They call the technique is called 'sit-and-spin'.
As to how the ATC gets stuck:
It means that most of my body is over the ledge and the rope is weighted but my ATC, due to the extension, is still on top of the ledge. Given the rope is weighted, it is difficult to make the ATC pass the over the ledge.