One of the most challenging parameters to estimate in leachate generation quantification is the percolation rate through a landfill cover. Since leachate generation is critical to operators, particularly when discussing walk-away aftercare conditionalities, this topic is still relevant. The best method for estimating the percolation rate of a cover involves placement of a lysimeter below or within the landfill cover to collect the percolating water. Previous work has focused on optimizing the height of the sidewalls of lysimeters to minimize the interference of its presence on the flow regime within the cover. Using numerical modeling, this paper examines the influences of climate, lysimeter geometry, and location, on the effectiveness of lysimeters. Robustness tests were proposed to assess the extent to which lysimeters altered the flow regime. The results show that lysimeter effectiveness depends on the relationship between its wall height, width, and depth within the profile. The lysimeters that passed all three performance robustness tests were considered reliable. Percolation measurement efficacies were found to be high when the height of the lysimeter, H, tended towards the height calculated using a simplified methodology based on steady-state calculations, Hlinear. For example, in the case of the cover soil tested and the Canadian climate, lysimeters whose H = Hlinear would not know any loss of performed for width to height (W/H) ratios greater than 3, no matter the depth it is placed. And it would lose only 5% in percolation efficacy for W/H = 2. In other words, a 3-m wide lysimeter would fit the bill in Canada. In the case of the Floridian climate, even when H = Hlinear, W/H ratios greater than 4 would be required for lysimeters placed nearer to the surface. When placed deeper, lysimeters with H > Hlinear perform better.