Discharges at several atmospheres are widely used for triggering combustion in cars. However, their properties are not well understood since the size and duration of the discharges become very small at high pressures, which makes the experimental approach more difficult. One possibility should be to infer the discharge properties at high pressures from those at atmospheric pressure, provided that the so-called discharge similarity rules work correctly. Thus, an attempt to check this validity is provided in this paper. Then, after establishing the exact conditions which preserve pressure similarity rules in non-uniform gaps, an example is given of two discharges under similar conditions. A departure from similarity is quite clearly observed. At several atmospheres, the streamer induced plasma channel, instead of developing the usual streamer filaments seen at atmospheric pressure, demonstrates a leader structure, i.e. the formation of a hot channel before the whole gap is bridged. Finally, reasons are given explaining that such a fast rise in temperature with pressure is indeed to be expected.