There will always be some gap between the fluid and obstacle. The higher the resolution the smaller it will be. Remember that the obstacle you use in the simulation doesn’t have to be the obstacle used when you render so you can fake there not being a gap at render time. There are many ways to efficiently use the fluid sim, covered many times in these forums and without seeing your blend cannot give specifics. Just to say make your domain as small as you need it so you don’t waste your resolution over a large un-needed area.