kenparry,
I found the bit I was thinking about in CAP804:
FCL.510.A ATPL(A) – Prerequisites, experience and crediting
.........
Of the 1500 hours of flight time, up to 100 hours of flight time may have been
completed in an FFS and FNPT. Of these 100 hours, only a maximum of 25 hours
may be completed in an FNPT.