The propeller is spinning at maybe 2,000 - 3,000 rpm.
The jet engine impeller is spinning at maybe 12,000 - 18,000 rpm.
BIG difference in reflectivity. The impeller will reflect a large percentage of incoming power. Anything that reads reflections will see the jet, assuming decent power to start with. The prop will be seen by anything that impinges enough power to pick up the small reflection percentage from the relatively slow-turning prop disc.
The Rolls Royce Merlin XX had a normal maximum of 3,000rpm and a reduction ratio of 0.42:1, so prop speed was 1260rpm.
The Merlin 66 had a reduction gear of 0.477: for a prop speed of 1431rpm.
The Griffon 65 in the Spitfire XIV had a maximum speed of 2750rpm and reduction ratio of 0.51:1, prop speed 1402rpm.
Early V-1710s had reduction ratio of 0.5:1, engine speed 3000rpm, prop speed 1500rpm.
R-2800s commonly had 0.5:1 or 9:16 reduction on 2800rpm. Prop speed 1400rpm - 1575.
Sabres IIA and IIB revved to 3700rpm and had a reduction ratio of 0.274:1 for a prop speed of 1014rpm.
The Jumo 004B had a rated engine speed of 8700rpm. The BMW 003 had a rated engine speed of 9500rpm.
The Spitfire IX had a 10'9" (3.28m) diameter prop. The BMW 003 was 0.69m in diameter - so the compressor was even smaller than that.
I don't know what this means for RCS. Generally, the turbine compressor is a more solid target than a prop, but it is also much smaller in area.