Not quite sure what you mean by: "If you normally work with 5RM loads"? That's a non-specific load; your actual 5RM load will vary on an hourly/daily/weekly basis depending on what you have been doing. I'm also not sure what you mean by: "Working true 2RM or even 4RM might take some learning"? Surely your 'true' RM for any rep range is whatever you manage when you test it? It won't necessarily be your RM in an hour, tomorrow, or the day after that. We train to drive adaptation to the imposed stress; we are hoping that our RM for any rep range is increasing but we don't know that it is for sure until we test it again. Sometimes accumulated fatigue will mask the effects of adaptation and we won't see increases in our RM's unless we allow time for the fatigue to dissipate first. With a standard HST cycle, you train with loads that are sub-maximal for any rep range for most of the time. At the end of a cycle it is usually possible to find new improved RMs. Your level of fatigue accumulation is lower than it would have been if you were pushing for every last rep in every session. That in itself is a good indicator that load is driving the adaptation and not fatigue.