Halo 5 Warzone Region Locked?

I’m a Singapore(Asia) player running expanded search preference.
When I try to solo queue in warzone I rarely tend to find matches and often get the “unable to match due to not enough players” notification.
However both yesterday and tdy, when I partied up with NA players though, I found matches extremely quickly and once they left I was unable to find matches again.
I guess this done to avoid laggy games etc, but I honestly don’t think it matters at least for social game modes.
Or am I analysing this wring way? Appreciate some insight please, thanks:)

Halo 5 doesn’t have a full on region lock, but it does try to meet a minimum standard for connection quality. Even social games deserve a minimum standard of quality. And as things are now, there can be some pretty laggy games in H5, so it’s pretty generous with connection quality already.