We investigate the best constants for regional fractional $p$-Poincaré inequality and in cylindrical domains. For special case $p=2$, result was already known due to Chowdhury-Csató-Roy-Sk [Study of Poincaré inequalities on unbounded domains, Discrete Contin. Dyn. Syst., 41(6), 2021]. addressed asymptotic behavior first eigenvalue nonlocal Dirichlet $p$-Laplacian problem when domain is becoming...