Yea lean during spool is typical, as it helps spool-up times. For example, on my Avenger (2.0L DOHC with a very large Holset HX40 turbo at 24psi on pump) I would tune very lean, 13.8-14.0 or so during spool, to help with lag. If your turbos arent quick to spool, your tuner was likely trying to help get things going -- running fat during spool would hurt even more.
These are the type of intricacies of the L-Series that Im interested in and need to learn. Different motors respond differently, back to my Avenger, we tend to tune very fat (11.0-11.4) at full boost because the 420a tends to make more power that way. If the L-series is happier and stronger running leaner, then ignore my comment above about fattening things up near redline.