Hi :)

The payouts depend on STEEM and SBD price. The higher the STEEM price, the higher upvote @tipU has so more upvotes can be made and by this more profit.

The higher the SBD price the lower the profit because @tipU has to make higher upvotes to ensure ROI +10% so less upvotes can be done.

If you have any more questions please feel free to ask :)