PLEASE ENSURE YOU USE THE HELITAPE PROVIDED WITH THE REAR MUDHUGGERS, INVISIFRAME AND ELECTRICAL TAPE ARE NOT SUFFICIENT TO PROTECT YOUR BIKES PAINT AND FRAME.  
SEE BELOW FOR HOW TO FIT VIDEO 
The Medium Rear Mudhugger is nearly identical to the Small Rear Fender, but 80mm longer. This longer version is ideal for most 27.5 full suspension frames. And 29” hardtail bikes.
If your bike has seat stay angles 28- 33 degrees then the Medium Rear Mudhugger is the probably the best choice, this applies to the vast majority of bike designs. Think Cannondale, Whyte, Lapiere, Transition, Rose, Commencal, Calibre, Kona, GT, Canyon (pre 2019), Giant and Marin.