The way DNS works under the covers (especially on mobile devices) is covered by the Happy Eyeballs RFC. Simple version… mobile devices query for an IPv6 address first and if no response in 20ms will issue a second query for IPv4 and only use the IPv4 response if it comes back first.
So short I’d intentionally making their IPv6 responses slooooow there isn’t really anything a DNS operator could do to influence the behavior.