I use the lat machine alternative as my gym doesn't have a GHR machine.
I usually do 4 sets of 5 (just started doing them) as my hams are clearly weaker than I thought and cannot manage any more than 5 reps.
I try to go down as slow as possible until I break fall, usually about parallel with the lat machine seat, which at that point I use my hands slightly to push up until I can bring the hams and glutes back in to it - usually only a very slight push is needed so the hams should be getting worked nicely.
However, I am never sore or feel like i've worked them as most articles suggest. Whereas straight legged deads leave my hams sore the following day, even within the 5-6 rep range.
Normal? Just keep doing them and try to improve the rep number?