Just pulled my 1250 apart and took a closer look.
The radius of the greater inlet size is 16mm.
The radius of the spindle holder is 11mm.
The 3 structs that hold the middle in place are 2.5mm x 2mm.
This gives a total intake area of:
201 - 95 - 15 = 91mm^2
The ID of the stock 1/2" outlet barb is 10.5mm, or 86.6mm^2.
So basically the inlet holes are less restrictive to the pump than the outlet 1/2" barb.
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