Help with Race Face diabolus cranks.

hello, having a spot of bother getting my diabolus cranks to install as per the manufacturers blurb. if i tighten them on to spec, they stiffen up and wont turn. i’ve tried different spacer settings, still stiff. so i have just tightened them up until they start to bind, then crank the cap down.. it seems alright so far.. does anyone know what im doin wrong, and will they be alright as they are. cheers.