The only thing that really affects the bubbles is whether or not there is surface agitation. If there is a strong surface current it will blow the nest apart, which is not really a problem. The farther water falls from the filter before it hits the water, the more agitation it will create on the surface. When the water flow is close to the water, it pushes the current under the surface more, but sometimes that is stressful to the
betta. I'd be more concerned about the Betta himself than about the bubblenest when adjusting your water level. You can create stiller areas for the bubblenest by using floating plants or tall plants that break the surface of the water.
Hope that helps
