The gain is given by \(G=\frac{V_{out}}{V_{in}} = \frac{R_3 + R_1}{R_1}\). Logically, if you want a high gain, you better put R3 >> R1.I was under the impression that it didn't matter which way round they went, however if they are ordered as they are in the last diagram i attached the output signal amplitude reduces dramatically so it seems to be right that they were reversed.