While doing research on belt temperature sensors, it alluded that belt temps will run higher if you snorkel the housing and if you are on a long downhill run. I can understand the longer length of a snorkel impeding the airflow since there is no fan but that shouldn’t be much. I however don’t understand how going downhill causes high belt temps.
There is a fan...it's the fins on the back of the primary and it moves a lot of air depending on RPM. I'm going to say neither statement is true. If there is no airflow restriction..such as using a 3"+ intake with NO filter, and the source location is the same temperature, and the discharge is also 100% unrestricted, the airflow volume and temps are unaffected. Going downhill only causes the clutches to shift-out a but farther thus slowing the primary RPMs which slightly slows the air movement...but downhill also puts less stress on the belt which means.. less heat so...I call BS on those that told you this.

The most heat is produced from the belt and clutch sheaves when it is under load and at higher RPMs.
A lot of people use 2" PVC and that will be restrictive for both sides because for example on my Z, the intakes calculate-out to just under 3". I went with all 3" ID turbo/inter-cooler pipe while leaving the discharge alone. I did add a dry-type filter which even clean had some slight restriction but not enough to worry about. When it gets plugged the temps go way up..that's why I installed an inline booster fan..to help cool it enough to get me back to camp. That didn't always provide enough so I then added a Donaldson Top Spin prefilter/particle separator which get about 60-70% of the dust out. Now I can ride all week and more without having to clean that filter or use the booster.