Born, I respect your job as a teacher and I applaud anything that helps to create discussion and further the learning process. So please view my comments in that context.
It is amazing how simple a refrigeration system is while being very complicated.
Actually I could argue that the suction pressure is only affected by heat, because by the laws of physics the pressure/temperature will always remain the same relationship. So when you say expanding vapor creates pressure you are right and wrong at the same time. I could say it is the change of state the creates the pressure. But without heat the liquid refrigerant would not change states and would flow back to the compressor as liquid.
Born, while in theory there may be a simple answers, in the field there is not.
You can not change any part of a refrigerant system without affecting the entire system. That is why it is important to look at the whole system.
Head pressure will affect suction pressure. Ambient affect head pressure. Air flow will affect suction pressure. Blowers, filters motor speed affect air flow. Humidity affects load. Any restriction in the refrigerant system can affect suction pressure including the necessary restrictor.