What is the opposite of "setting the bar"?

Defining such a level or limit is setting or placing a cap or to cap as a verb.

From Lexico:

‘council budgets will be capped’
SYNONYMS set a limit on, put a ceiling on, limit, restrict, keep within bounds
curb, control, peg
‘The legislation, however, does not place a flat cap on the value of the homestead exemption that an individual can exempt in bankruptcy.’

"Explain to him that he should cap it at five thousand pounds" would mean not to exceed that amount and to pace himself accordingly. His coworkers might tell him not to break the curve, but that doesn't work as well for your second example. Both are related to quota and distribution.

"When I am saying "fifty cold calls a day," I am setting the bar, not capping it at that/not placing a cap on it at fifty" would mean that while fifty calls are expected, that number isn't the ceiling. It's not the cap, so feel free to keep going.