Heart rate recovery questions

I 've been working out for years, but I just recently came across this
"heart rate recovery" thing. It makes sense to me that the rate of recovery should be a relevant measurement but it seems to me that the sources I've found on it lack a sensible basis.

They talk about number of beats recovery, instead of percent. (40 beats recovery in 2 minutes, is not the same thing for a person who worked at 140, versus say 180). The duration and type of exercise usually isn't mentioned.
If you do a 30 minute workout, your muscles are more tired and continue demanding blood to a greater degree than if you worked out 10 minutes, or just worked long enough to be breathing hard..

That said,
1] can anybody furnish me a good source(s) on HR recovery that makes more sense than these medical research things I've come across?
2] in my case, my resting HR is 45; max is 200?; and after 27 minutes of exercise at 160+ (appx 80% my max), my recovery after 2 minutes was a 40 beat drop. Is that good, bad or indifferent?