When a sprinkler head is behind a shrub it cannot cover the area needed. It is best to use DRIP line irrigation in shrub beds to have as close to 100% coverage as possible. As long as you do not run to long and create run off. Be careful of this. You will also receive as close to 100% of the water applied as opposed to wind blowing it all away or evaporation. We highly recommend NOT raising the sprinkler head above the shrub. This only causing over throw and limits the amount of water on the root zone. This also will give opportunity to water setting on foliage possibly causing fundal issues on certain plants. Lots of water waste doing this as well. If you do not want to invest in DRIP it is best in most cases to lower the head and allow it to spray through the root zone area. I good evaluation is needed to determine the best solution.