The classification part of the call number is in 852$h in the LHR. The item part is in 852$i.
If you format the label setup as shown below, the call number will only be split into two lines:
Here is an example LOC call number in this format:
BT1500
.A12 1999
If you want to split the call number into four lines, format the label setup as shown below:
Here is how that same LOC call number appears on the spine label now:
BT
1500
.A12
1999
The "Data" content type pulls information from both 852$h and $i. This content type has a built-in line break that depends on the number of characters, length of the call number, size of the label, etc. It typically works best for narrower spine labels, such as A12360, L7651, and SP1.