I have a shot size issue I need sorting

I just picked up a EMCO 1/3 oz bench top injection molder and my output is much less than expected..
By my math I should have a max shot volume of 9.72cc (9.35 grams of PS at 1.04 g/cm3) I made a mold that should have fit it.. Cavity volume of 8.31CC
but running in high melt PP (RTP 199X 106829 J) I am getting a 4.5-5.2 gram output , SG 1.02 so 4.9-5.3 CC and its no were near filling the mold.

Where did I go wrong with the math or what could be causing my issue?
The current output is not very useful

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