I as well have a bit of experience being a Radar
RCS is everything.
The amount of reflected energy from the target (our boats) is effected by the two way range from the Tx to the target i.e. R squared out and R squared back, by the RCS (radar cross section) of our boat
, the originating transmitter power (which itself is effected by transmit pulse width sometimes selected by the user) and the receiver STC (sensitivity time constant) curve that varies the radar receivers sensitivity based upon range. Of course the sea state will have an effect but other than saying rough seas make it harder to detect not included in the list. The recreational radars give us a lot of fiddling power over the STC curve and they choose to call it gain, weather
filters etc. Be careful if you take the receiver out of auto and begin to tweek sea state filters, ocean vs harbor gain settings and the like.
My advice is get the largest corner reflector you can stand to look at and you will be seen next to your neighbor far sooner. Improve your boats RCS.
Anything that reflects back energy is better than nothing.
Regarding the radar transponder comments, we may be thinking about a "radar beacon". Last time I entered NY harbor from the South there was one that would transmit each time my radar lit it up. Very effective because it will fast tune to your transmitters frequency and then re transmit back to you.