Lower Back Burn When DL'ing

Hey guys, I am at the fifth wk of ABBH I and I was wondering if what I am doing is right. When I deadlift, 5 x 10 at 65% of 1RM, my lower back seem to get a hell of a workout, I can really feel the burn there. But when I do 10 x 5 at 80% of 1RM, my lower back doesn’t feel a burn. I was sweating like hell with 5 x 10 and not so much sweat with 10 x 5. Is it my form?