Air stone position and bubbles question

[FishguyAU]

Hi All, Just wondering if the air stone should be positioned as close to the gravel as possible to increase aeration, or should it be closer to the surface? Also, are air stones that produce small bubbles more effective than large bubbles? Thanks!

 

[BigManAquatics]

I usually set them on the substrate or partially bury them, if i don't use them in a sponge filter.

 

[Ksway]

Down at the bottom of the tank, also small bubbles would be preferable but any bubbles at all will certainly help. Why not just add a sponge filter to it as well for more bacteria and water clarity.