The RM1SG is not recommended for an increase in range per se, but because it is very wideband compared to the HiMark superhet, it is likely to receive better from poorly tuned X10 transmitters. This might seem like an increase in range to those who were having troubles with certain transmitters. You are right that an improved antenna is needed for a true range increase.
On my transmitting devices, MS10A, DS10A, MS16, vt38a (motion floodcam) I found that I can extend the transmit range by about 10 feet by inserting an 18.5 inch wire into the coil. This seemed to work for about 1 in 4 devices or so because the extra transmission wire tweaks the signal just a bit. It seems that if the device was poorly tuned to start with then the extra antenna just made it worse.
However aftter doing the RM1SG mod, I now 100% working devices all with the transmitting antanae mod.
Combined with the egg beater antanae on the on the cm15a, I no have issues with these wireless devices having poor signal.
I took apart the ss13a sticky wall switch, but there is not coil to attach a wire too, so I have to experiment with that a little bit.