The "first mounting" for a young Icelandic Horse is a semi-mount; just having the rider lean their weight on the top of his back, supported by a mounting block. Slow exposure, quit before he quits, give him some rewards.

Susan says: Here is a video of when I first laid across Andi's back.

Susan's Mom is the wonderful camera person for these sequences. (Thanks!)

I realized after I was flopping around on his back that I did not have my helmet on, plus I needed something to hold onto to put my full weight on him. So I put on the surcingle and my helmet and we did my full weight on him. You can see how concerned he was.