OK, let's see how things work when we make the strip very wide indeed. Below are the results for 40cm-wide strips with a single fibre (MINOS-style).
The black curves shows the survival probability for a 1cm-thick strip, while the red shows a 2cm-thick strip. Apparently, you win with a thinner strip for p.e. per MeV, but of course you lose overall because a thicker strip gets more MeV.
Interestingly, the tails of the distributions are well modelled by a Breit-Wigner form. At the very edge of the strip it doesn't work (since the sides of the strip reflect some back, raising the outer part of the tail). The central peak isn't well modelled: this is due primarily to photons that undergo only 0-1 bounces before hitting the fibre.
Note that this particular simulation doesn't include the fibre acceptance; this is just the odds you'll hit the fibre. The disribution looks very similar for the more rigerous case; statisitics are just a lot worse.
