  We improve the residual based stabilization technique for Signorini contact
problems with Tresca friction in linear elasticity solved with $hp$-mixed BEM
which has been recently analyzed by Banz et al.~in Numer.~Math.~135 (2017)
pp.~217--263. The stabilization allows us to circumvent the discrete inf-sup
condition and thus the primal and dual sets can be discretized independently.
Compared to the above mentioned paper we are able to remove the dependency of
the scaling parameter on the unknown Sobolev regularity of the exact solution
and can thus also improve the convergence rate in the a priori error estimate.
The second improvement is a rigorous a priori and a posteriori error analysis
when the boundary integral operators in the stabilization term are
approximated. The latter is of fundamental importance to keep the computational
time small. We present numerical results in two and three dimensions to
underline our theoretical findings, show the superiority of the $hp$-adaptive
stabilized mixed scheme and the effect induced by approximating the
stabilization term. Moreover, we show the applicability of the proposed method
to the Coulomb frictional case for which we extend the a posteriori error
analysis
