There are a few situations/items that negatively or positively effect PE, my suggestion is to change these effects to modifying vision range directly instead, these include;
Stealth, Night time (may already be just vision), mentats, psycho, blindness and crippled eye effects.
The reasoning mostly is so that the positive and negative effects on a characters perception are always somewhat effective e.g. psycho/blindness with PE 1 still reducing vision, mentats with PE 10 still being useful etc, but particularly blinding and eye crits, which in theory do nothing to someone already with 1 PE.