How does dnsmasq proxy dhcp work?

Question

linux

There is an nfs server for downloading over the network without flash drives. Used dnsmasq with dhcp proxy role as there are already 2 main dhcp servers on Windows.
In one network segment, everything works fine, clients are loaded and everything is fine.
But as soon as I try to start clients from a different subnet, nothing happens.
Although I added a second range and did ip helper on L3 Tsisk for my server, I see in the logs that the client is visible, receives options, but the tftp download does not continue. I tried to move
my server to the client subnet with In this case, the main dhtsp servers remained in the "server" subnet.
Clients started to load, but for some reason it does not receive the default gateway and the local address link appears in the routes.
It seems to me a routing problem, but in which direction to dig without a clue
Can someone explain in detail how a dhtsp proxy works?