Add the heptane slowly by couple of mls at a time, dont shake it all, instead just let the warm heptane do its thing, just make swirling movements. As you add the heptane you should see a darker layer forming. Dont add so much that it all dissolves, rather add till you see most dissolved but dark layer is on the bottom.
This amount should usually be around 20-30ml per g, yeah, but maybe for some reason yours is dissolving "better" (Too hot heptane? Too much shaking? Heptane has mix of other solvents in it that dissolve dmt better?). So instead have the 20ml just as an idea but go by the looks and without shaking.
Remember to add a bit more heptane to the dark goo to dissolve more of the stuff in the goo, and freeze separately, for second quality but still very active crystals