Just a side note seeing your oscilloscope curves: when you have a fast charge time and a slow discharge time, as it seems that you have, using TWO probes each near to two different charged capacitors, remember that those two probes create a circuit path between the two capacitors (probe tip 1, its internal resistance, its ground == ground of the second probe, internal resistance of the second probe, probe tip 2). In real life, that path won't be there. You can simulate the oscilloscope path on Spice adding the two 20MΩ resistances to see the curves that you got on the scope are... scope artefacts. Here, such an artefacts: