Finally, we study the effect of the position of the surface S on which the Reynolds equation is solved, see Fig. 3. It is seen in Fig. 8 that the solution depends weakly on parameter α specifying the position of S between the lubricated boundary γl and its projection on the rigid countersurface, Pðγl Þ. For Uη ¼ 0:1 N=m, the effect is hardly visible, and it is negligible for lower sliding speeds (not shown).