MPEP 2144.05.II.A explains (with citations reduced for improved readability)
II. OPTIMIZATION OF RANGES
A. Optimization Within Prior Art Conditions or Through Routine Experimentation
Generally, differences in concentration or temperature will not support the patentability of subject matter encompassed by the prior art unless there is evidence indicating such concentration or temperature is critical. "[W]here the general conditions of a claim are disclosed in the prior art, it is not inventive to discover the optimum or workable ranges by routine experimentation." In re Aller, 220 F.2d 454, 456, 105 USPQ 233, 235 (CCPA 1955).
So, according to the MPEP, the applicant has an uphill battle when claiming within a parameter with a certain value or within a certain range. However, if the specification (or other evidence such as a declaration) can establish certain facts, then the uphill part may not be so bad or even necessary in the first place. Attacking the recognition of a parameter as being recognized as result-effective can often be the most powerful approach (assuming the facts apply). One reason is that the burden still lies with the examiner to establish a prima facia case of optimization, and they cannot do that if the prior art does not recognize the variable as result effective.
Specifically, the prior art must have recognized that the parameter in question is one to be optimized in the first place. From the MPEP:
B. Only Result-Effective Variables Can Be Optimized
A particular parameter must first be recognized as a result-effective variable, i.e., a variable which achieves a recognized result, before the determination of the optimum or workable ranges of said variable might be characterized as routine experimentation.
Be careful here as the prior art does not necessarily need to recognize the same advantage as the applicant (unless the applicant is somehow claiming a certain result is achieved). Nevertheless, the prior art must teach that the variation of the variable in question somehow is relevant to a performance objective and thus should be adjusted or optimized through routine means.
Alternatively, if the applicant tries to establish criticality of the particular range, the applicant now has the burden of coming forward with evidence, usually of unexpected results. The applicant can also come forward with evidence of teaching away. Here, the evidence must directly correspond to the cited art and/or the claimed parameter/range.
So, when drafting an application, if there are any particular parameter values or ranges of interest, make sure to at least provide some evidence that can support unexpected results later on. Or if you are in prosecution without such evidence, consider whether a declaration can provide the convincing evidence you need.