the maharsham indeed defends the minhag in chelek 1, 175. He aays this is based on shitas ha’taz, that you make a bracha achrona on a shot glass of yayin saraf (schnapps) even though it’s less than a revi”is, because it’s considered choshuv. So too by kidush, where chamar medina is acceptable, a shot glass of this sort of chamar medina is considered choshuv.
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