According to one information of the Czech Heritage Institute Karl Mattusch was based in Karlovy Vary. We have just a few information about him. It is documented, that Mattusch designed the catholic church in Potůčky, Czechia in 1911 and a house in Žilina, Slovakia in 1925. He was most probably in contact with architects in Prague, because the house he designed in Cheb is stylistically connected to the architecture in Prague.
Sources
Buildings
Cheb, Czechia
Germania