No, it is the other way, the length is the number of elements of the destination.
The instruction calculates the number of bytes to copy by multiplying the number of bytes of the destination's data-type by the length specified, then it copies that number of bytes from the source to the destination.
COP, CPS, and FLL can be very destructive if you get your length specification wrong.
If the destination is a single tag, then you are protected against having the length too long, because the instruction will terminate when the destination tag has no more space for data.
But if the destination is an element of a structure (UDT) tag, then those instructions will trample over the following elements within that structure.