I was noticing this was still a bit tricky even after the kameo + ex move change and I think it's because you can't input ambush kameos during blockstun and by extension, during a reversal window. From what I can tell, summon kameos can be buffered and will come out frame one, but ambush inputs will just be eaten. So you have to wait for the startup of db3/ex db3 to input u+kameo, not before or at the same time like if you were just letting it rip in an open state. This can make the kameo call missable on stuff with funky long blockstun (something like Havik d4) because you kinda have to manually time the kameo call depending on the blockstun and it's easy to be late after ex db3. I'm not 100% consistent in landing u+kameo so not sure if I even fully understand it but hope this helps.