Thanks Michael and Mark.

Michael, have a look at figure 4 here. It shows graphically what I thought happens to the curve's shoulder with increasing development times. Basically the shoulder moves up and to the left of the HD curve (Dmax of the film eventually causes the shoulder to clip as dev time is increased). Two other examples. Here showing the HD curve for TriX and another example using AZO paper (which I assume could be applied to film in general) here in chart 3 . Both show the shoulder moving up and to the left with increasing development time. If I draw a vertical line say mid way along the straight line portion off all those curves and then start moving to the right (up) each curve, one will traverse a longer stretch of the straight line portion on the traces with less development. Note that I'm not seeking to shift the exposure range down the curve, I always lock the exposure range to the horizontal axis. Less straight line portion this means less over exposure latitude.

Finally on p. 230-232 of WBM 2e there are also some pertinent notes on Exposure Latitude. Near the end of p.231, we read "when in doubt it is better to err on the side of under-development allowing for more exposure latitude".

regards
Peter