Shop heads like the ones in the photos are caused by just two things.
Technique - the squeezer not being perfectly aligned with the shank of the rivet at the start of setting, or the squeezer being allowed to tilt while squeezing.
The rate it is squeezed (air pressure used) can have a small influence on this because the faster the plunger moves, the harder it can be to maintain alignment.
Rivet length - The longer the unset rivet shank is, the harder it is to set it straight with a squeezer (with a gun and bucking bar it is usually less critical).
This is why there is often criticism of the rivet lengths called out in the plans. If a specific rivet length is going to be just a bit on the long side (based on the 1.5XD rule of thumb, the next size smaller will often be specified if it will still produce a shop head that meets the MIL SPEC
Using this very slightly undersized length has a major influence on the ease of forming a proper shop head.
If you chose to use the next size longer rivet than specified, it is at least part of your problem.
This is not to say that the plans specified rivets should always be used without question. Mistakes can be made, and the builder is the final quality control decision maker.