Based on Jerm's suggestion, the way the length modifier worked for me was as follows....
1) Hold L1 or R1
2) Press Length selection button (i.e. short, good, full, Yorker)
3) Release L1 or R1
4) Usual bowling sequence from here...
What this meant was that now I could deliver at 12 different lengths rather than the 4 previously (see the pitch mat pics above for illustration).
Has anyone been consistently getting edges to slips (not WK) off front foot drives or defensive shots? Only slips catches I've gotten are off late cuts, which aren't really edges.....