已知边长为\(6\)的正方体\(ABCD-A_{1}B_{1}C_{1}D_{1}\)，\(E\)，\(F\)为\(AD\)、\(CD\)上靠近\(D\)的三等分点，\(H\)为\(BB_{1}\)上靠近\(B\)的三等分点，\(G\)是\(EF\)的中点．
\((1)\)求\(A_{1}H\)与平面\(EFH\)所成角的正弦值；
\((2)\)设点\(P\)在线段\(GH\)上，\( \dfrac {GP}{GH}=λ\)，试确定\(λ\)的值，使得二面角\(P-C_{1}B_{1}-A_{1}\)的余弦值为\( \dfrac { \sqrt {10}}{10}\)．