Watch the Kick & Slap Approach online guitar lesson by Dmitry Lisenko from Percussive Acoustic Bass (Foundry)
A very common approach to playing is to perform kick and slap at the same time. When you're doing upper kick, try to slap a note with your thumb. It's similar to standard slap technique, except that usually to get a sound, we rotating our wrist. However, here we're moving our whole hand to add a kick sound. Avoid delays between slap and note and also keep good balance of these two elements.