Should be more, or less & please explain. Thank you.

Should be a personal choice reflecting many factors. I think a Domme who gets intense pleasure for taking control, being more meaningful for her than the pleasure that a FS escort gets from an encounter, might want to set the donation a little lower to encourage more volume. Similarly, a client who gets something much more from a Domme than he experiences with GFE might want to offer a bit more. In my limited experience, the menu offered in BDSM is very wide ranging. I don't see why a relatively plain vanilla experience should be as high as the more complicated, equipment intensive or physically demanding of the Domme, and perhaps also distasteful to her. Personally, I will offer more for GFE because I don't get that extra "bounce" from BDSM. One person's observations.  

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Totally depends.    
Equipment, planning and logistics are more complicated for BSDM.
If it's strictly BDSM and there's no sexual component, then it's more of a straight forward service.  Less taxing most likely.

If it's a combo of GF/BDSM, then I think it warrants a higher charge.  
There are a lot of moving parts, planning, higher risk to her health etc.