Voltage glitches are a fault injection technique that aim at disrupting the power supply such that the data or instruction flow in a chip can be modified. In 2019, a new class of voltage glitches was introduced based on arbitrary voltage supply waveforms that are generated by polynomial interpolation over randomly chosen points. Despite their demonstrated success in practical studies, many questions remained unanswered, e.g., what are the relevant characteristics of the waveform that enable this success? To answer this, we investigate the waveform generation process itself, prior to applying any type of automated search. In addition, we perform an in-depth analysis of (non-)working voltage glitches. Furthermore, we introduce the notion of specificity for glitches, by studying how waveforms can be generated that achieve very specific goals, such as a double instruction skip. We compare our results based on a real-world benchmark for firmware extraction and demonstrate that our insights lead to a reset/success ratio that is improved by a factor of 13.5 compared to previous work. This amplifies the threat of this class of voltage glitches.