You can over kill soft sponge. 37 degree is on the soft end booster can kill it.
Like I said in many other threads, Chinese fans had batch tested the hardness of commercial H3. They are rubbish.
You buy 5 sheets of 37 degree commercial H3, the true hardness can range + or - 2 degree. Your friend's 37 degree could be a 39 degree who knows.
Same as provincial H3. QC is a bit better but still sucks.
To have true consistency you need the National version.
My method is to now glue any commercial H3
on my blade without boosting because one really can not tell anymore what hardness it is . After this initial "cold run" I then decide how much boosting (if any) I feel is needed.
I cut my rubbers with scissors and leave a generous 3-4mm overhang so it is then easier to place back for the second gluing.
I found one can not rely on what is printed on the cover as hardness ,just because it sold as a H39 means very little and I also had Rubbers that came with a sticker over the original print on the covers that would (for example) correct a 38 to a 39 etc.
Still, having moaned about it, and even though they are not as sticky anymore as they used to be, I regard the commercial H3 as great rubber at a decent price, good enough for any club play and also some tournament players.