I have said this before but I am going to say it again. 80 % of engine failures are caused by the actions or in actions of the pilot. The best situation is to not have to choose a field because you did not let the engine fail in the first place or if it did fail you were able to recover power by use of an effective and fast engine failure cause check.
For instructors: Before your students get to fly a practice PFL they should have to master the initial vital actions, including be able to quickly establish a stable and trimmed gliding attitude and can with out prompting or faffing about perform the engine failure cause check.
I think this fixation with flying the perfect forced approach is partly rooted in an unstated rather prevalent "hero pilot syndrome". In that most pilots want to be the guy the others talk about at the club bar. "Oh blogs there had an engine explode on him with no warning. He coolly squeezed the machine into this tiny field with no damage at all !".
Instructors need to beat this fantasy out of the students head. Safe flying comes with proactively identifying and eliminating those boring and unsexy things that history has shown cause the majority of engine failures like carb ice and fuel exhaustion/mismanagement/contamination, and practice the checks that will restore power if performed quickly and properly. Then yes they need to know how to fly the aircraft to a controlled touchdown at a chosen spot. Mary, the OP IMO nailed the field selection criteria.