Experience?

The pushrods have to be aligned into the sockets in the rocker arms. I usually do this after I get a bolt into holding the cylinder in place.

The small end of the pushrods go towards the rocker arms.

If the tip of the pushrod is caught on the lip of the adjuster on the rocker arm there will be no compression.

If the engine is all together, the carburettor must be fully open in order to properly judge the compression feel.