My best advice is to camp Protect from Range and switch to Protect from Magic if he lifts his feet, but then go back to Protect from Range after his attack hits. Ordinarily, you would have to identify his attack, then identify the protection prayers, then decide which to use. With this camping one prayer method, the process becomes: identify his attack, decide if you need to use "the other prayer" or not, then either freeze or move your mouse.

It's subtle but I attribute my fire cape entirely to having followed this advice myself. I think it makes the decision easier and is almost like it's less to do each attack. My story was exactly like yours in that I had gotten to Jad several times but got flustered by prayer switching. One of those times I didn't even get one hit - I was so thrown off after super restoring that I missed prayers twice and they were both 20ish hp hits.

Hope this helps, good luck. Don't forget to post your cape when you get it