  We give an intuitive geometric explanation for the apparent breakdown of
standard finite-size scaling in systems with periodic boundaries above the
upper critical dimension. The Ising model and self-avoiding walk are simulated
on five-dimensional hypercubic lattices with free and periodic boundary
conditions, by using geometric representations and recently introduced
Markov-chain Monte Carlo algorithms. We show that previously observed anomalous
behaviour for correlation functions, measured on the standard Euclidean scale,
can be removed by defining correlation functions on a scale which correctly
accounts for windings.
