In Fast RTPS, you use multicast just for participant discovery (so “SPDP option” is not required, EDP is going to be always using unicast), and we have a very defensive defaults for this kind of networks. After Intel and others reported some problems over wifi on navigation, we reacted modifying the discovery behaviour, and changing the default parameters, some months ago, so that is already on place.
With those settings (now the default), our performance is really good. See this video from @rotu:
This is the case you are talking about, I think.
When you need to improve even more this behaviour, because multicast is not an option in your network, then you should use the discovery server or unicast discovery.
The Discovery server is included in Fast RTPS, any node can be a discovery server, you do not need anything more. And we can find easy configuration options. Right now, it is as simple as this:
But we can even go further. I have no particular problem in making this discovery mechanism the default.