Apply Alex's suggestion

src/pyhf/pdf.py

@@ -610,7 +610,7 @@ def expected_data(self, pars, return_by_sample=False):
         # Verify parameter shapes
         if pars.shape[-1] != self.config.npars:
             raise exceptions.InvalidPdfParameters(
-                f"eval failed as pars has len {pars.shape[-1]} but {self.config.npars} was expected"
+                f"Evaluation failed as parameters have length {pars.shape[-1]} but model requires {self.config.npars}."
             )
 
         deltas, factors = self._modifications(pars)
@@ -715,7 +715,7 @@ def expected_auxdata(self, pars):
         # Verify parameter shapes
         if pars.shape[-1] != self.config.npars:
             raise exceptions.InvalidPdfParameters(
-                f"eval failed as pars has len {pars.shape[-1]} but {self.config.npars} was expected"
+                f"Evaluation failed as parameters have length {pars.shape[-1]} but model requires {self.config.npars}."
             )
 
         return self.make_pdf(pars)[1].expected_data()
@@ -744,7 +744,7 @@ def expected_actualdata(self, pars):
         # Verify parameter shapes
         if pars.shape[-1] != self.config.npars:
             raise exceptions.InvalidPdfParameters(
-                f"eval failed as pars has len {pars.shape[-1]} but {self.config.npars} was expected"
+                f"Evaluation failed as parameters have length {pars.shape[-1]} but model requires {self.config.npars}."
             )
 
         return self.make_pdf(pars)[0].expected_data()
@@ -765,7 +765,7 @@ def expected_data(self, pars, include_auxdata=True):
         # Verify parameter shapes
         if pars.shape[-1] != self.config.npars:
             raise exceptions.InvalidPdfParameters(
-                f"eval failed as pars has len {pars.shape[-1]} but {self.config.npars} was expected"
+                f"Evaluation failed as parameters have length {pars.shape[-1]} but model requires {self.config.npars}."
             )
 
         if not include_auxdata: