[Bug]: Particle size distribution concentration plot x axis may be incorrectly labelled or calculated

[TomTranter]

PyBaMM Version

22.7

Python Version

3.9

Describe the bug

Steps to Reproduce

import pybamm
model = pybamm.lithium_ion.MPM()
sim = pybamm.Simulation(model)
sim.solve([0, 3600])
sim.plot([
    "X-averaged negative particle concentration distribution",
    "X-averaged positive particle concentration distribution",
    "Terminal voltage [V]",
])

Relevant log output

No response