Nasal Mask fit question

If I wear medium Resmed nasal masks?.... Mirage Ultra 2, and Mirage Micro...... Am I safe in ordering a medium Respironics Comfort Gel mask?

I say not necessarily. Check the https://www.cpap.com and look up the smask. Often they will have a sizing guide/chart or template that you can confirm the size.

I would also order the mask insurance to ensure that if it doesn't fit that you can return it and get the proper size.