Isn't Spas-12's chest armor also big?

It implies that Spas has gained weight but SAT hasn't.

SAT8 is supposed to be 156 cm. Is SPAS even shorter? She must be tiny in this pic.

Rhekatan said:

SAT8 is supposed to be 156 cm. Is SPAS even shorter? She must be tiny in this pic.

According to the Chinese wiki, her character designer says that SPAS is 162 cm tall. Probably an artist error.

Half-Life reference with SPAS using a crowbar?

Crowbars are a common "improvised" weapon, so no.