Ramps are a problem in manual wheelchairs – what if you get stuck halfway and your grip starts slipping? You need never be there again.
A cautious person would choose low gear and RUN mode before starting the ramp. Then go until you get tired (you probably won’t, with the power of RUN mode) but, if you do, just stop. The chair will not roll back. When you are ready, you can just keep going.
If you are young and foolhardy and attack the ramp in a high gear, just stop when you get tired and move the gear levers to a lower gear and go again.