Broiling Specifics

The recipe means that top top of your chop should be 4-5 inches from the element, however broilers vary a great deal so I would use that as a guideline and not a rule. This ties in with your second question about setting, as the answer depends on the performance of your broiler.

There are broilers that can barely melt butter on the high setting and others that will reduce a steak to a sad pile of char in minutes on the low setting. Most are in between those extremes, and the only way to know how yours performs is to cook on it. I suggest you cook a bunch of something inexpensive on it first, burgers would be my choice as they are red meat and will therefore give you a good idea as to how lamb and steak will be. Experiment with heat settings and distances until you get the result you want.

For a thinner lamb chop you will want high heat for a shorter amount of time as it will brown the chop without overcooking it. For a thick chop you want a medium heat for longer unless you want it really rare, at full blast you may burn it before the inside is done.