When does a unit go "under" an entrenchment?

[saracv3]

A most interesting situation has emerged with my entrenment attacks in AOI #4.This scenario calls for the Allies (SA/British) to capture six Italian entrenchments; two on each board. The opposing forces appear very assymetrical. The Allies have 82 counters (leaders included), while the Italians have 27 counters (leaders and entrenchments included.) Bit the Allies are hampered by special rules dividing their forces. They also don’t get the major balance of their force until turn 12.
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The South Africans started by attacking an entrenchment on turn 4 using 2 infantry platoons and a leader. (9 attack points) against 16 Italian pts. However, I read the stack wrong and thought the Italians had 3 infantry platoons comprising the stack. In fact, there was a HMG unit instead of a infantry platoon. I rolled a 12 for First Fire. Result = X.

Question: Should I have rolled on the Direct Fire table instead of the Assault table?

I’ll tell the rest of the story after I get some response here.