I was wondering if the same benefits of IBT are experienced when inclining the bed from only the waist up? In other words, does the bed need to remain straight head to toe in order to get the benefits of IBT? We are considering the Sleep Number bed but I don't believe it can raise the head of the bed while keeping the entire bed straight. Another question would be...like a hospital bed, does raising the bed (bending at the knees) negate the benefit of raising the head? Thanks.