Note that LPD comes in two forms, powder and liquid concentrate. The powder seems to be much more popular because it is, naturally enough, considerably less expensive (and also keeps practically forever before mixing, I would think, since it comes in a metal can.) The liquid is, also obviously, very convenient though. The liquid is twice as concentrated as the powder. So for the concentrate they recommend 1+4 dilution for normal tones, 1+2 for cold tones, 1+6 to 1+8 for warm, where for the powder mixed to stock they recommend 1+2 for neutral, 1+1 or full strength for cold, 1+3 or 1+4 for warm.
I happen to have both a (half used) bottle of concentrate and an unopened can. This talk of replenishment was new to me so I just checked the labels. Both say to write for a brochure on replenishment.