unclear tariff parameter bandwidth call in charging strategies

individual optimization and charge on arrival strategies include a reference to a tariff bandwidth, currently written as household.tariff.rules[0].capacity_bw (lines 147 and 199 in models.py)

if capacity bandwidth is not the first in the list of rules, this would fail. Furthermore, it is hard to ascertain from the code what rules[0] is. Could this be made more explicit and fail-safe?