I am not a dwarf breeder, but I believe
@Preitler is right. I am hoping another dwarf breeder will chime in, but I think this is a case where there is such a thing as too much of a good thing. You can breed a true dwarf to a slightly larger "dwarf" that does not stay under the max weight and some of those babies will stay small and some will grow to be too big. Or you can breed 2 dwarfs and all surviving babies will stay under the max weight but a proportion will not survive, or something like that. The non-surviving babies look like runts with oversized heads, hence the nickname "peanut". They can survive for a short time before dying, or they can be stillborn I believe. Someone who has bred dwarfs should clarify the exact ratios here....
@ladysown aren't you breeding hollands?