There is no such thing as too much space. You can have only 6 birds in 25 square feet if you like and they will be very happy. Just make sure they have plenty of hiding places. The should have a minimum of 1 square foot per bird. I keep about 12 per 20 square foot pen.By what you say that if the flock is big enough you can give hens 4sqf per 1 hen but can it be done with quail? If I have 25sqf(which is good for 25 quails) could I possibly add another 10 or 20 quails in that space for them to still have enough room to be happy? If It can be done with quail I guess then they're just better for eggs comapring to hens. Of course more cleaning is needed.
25sqf of space can't house 6 Hens since the flock is too small but it can house maybe 3 hens that will give me 1-3 chicken eggs daily
25sqf can house 25 quails which will give me around 3-4 chicken eggs daily. But since quail flock of 25 is bigger/more space for them
maybe if I add 10 or more quail then I'll get 1-2 chicken size eggs.
BTW, when you say "hens", I assume you mean chicken hens? Quail females are called hens too, as are several other species of bird females.