The cable to the signal transmitter is simply too short. I get it (normally on the handlebars next to the bell) connected only to train with my 28er touring. Especially with a suspension fork can not go well the long. From the look of the free standing taut lines to mention! The old Sigma speedos had here at least more accessories in extra-long variant. Other manufacturers give the same lump to 20-30 cm, so it is nice to wrap the cord around brake lines etc. But the current Sigma tachometer there is neither one nor the other. Incidentally, exactly the same with the cadence signal transmitter. Here is probably saved systematically on material. Too bad!
Only buddy Irons has here can then help. 30cm cable to shrink tubing to water and off it. As the Sigma speedos do not work with resistors but with pulses, which is not an issue. Now it is also (reasonably) on my "huge" 28er bike.