According to my research on information technology and it's hardware, I can say that based on the information provided within the question the technician is most likely to use a Mini-ITX case. This is because an HTPC is a A Home Theater PC which does not need all the hardware that a regular PC needs, just the minimum specs, and these devices are usually hidden away in a drawer or behind the TV. Therefore he needs the smallest PC case which is a Mini-ITX.
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