Yeast calculators are about as useful as toilet paper when it comes to propagating yeast cells. Yeast cells are living organisms that behave differently in different environments. The only way to know how a yeast culture is going to behave in one's brewery is to use it and take very good notes.
As I have said many times, the difference between a 1L starter and a 2L starter is approximately 90 minutes of propagation time, making the argument for a 2L starter when pitching normal gravity beer a non-sequitur. Now, the difference between a 1L starter and a 5L starter is log(5) / log(2) * 90 = 208 minutes, or 3.5 hours of propagation time. However, one is looking a step rate of 22 / 5 = 4.4 when pitching the cells from a 5L starter into a 22L batch of wort. It takes approximately log(4.4) / log(2) = 2.14 replication periods to reach maximum cell density when pitching at that rate. In practice, we should step between 10 and 20 for most batches, especially if we plan to repitch the slurry. Pitching at a higher rate than that tends to lead to declining culture health, as the average cell age increases with each pitch.
The key to successful fermentation is to pitch enough healthy cells at the peak of their performance into well-aerated wort to get the job done. The osmotic pressure difference between the cell contents and 1.056 wort is not high enough to cause dehydration and loss of turgor pressure, resulting in cell shrinkage and wrinkling of the cell plasma membrane as happens when one pitches a starter into 1.080 wort. Additionally, the solubility of O2 decreases as wort gravity increases (Henry's Law). In essence, we have to pitch a higher number of cells when pitching high gravity wort because of cell loss coupled with lower growth rates and cell health due to lower gas (O2) solubility.