https://www.arin.net/policy/nrpm.html#four10 

This policy specifically envision the day when smaller than /24 blocks become routable and/or there could be non-routed needs for globally unique IPv4 addresses, in either of those cases it would be wasteful to assign a whole /24.  Currently if a routable block is needed, which is typically the case, ARIN's operational practice is to assign a /24.  However, if or when, smaller blocks become generally routable, no policy change is necessary for ARIN Staff to change it's operational practice.  

Further, it should be noted that to access that pool of IPv4 resources, a justification as to how the IPv4 addresses will be used to support the immediate deployment of IPv6 is necessary.  Use of that pool to simply deploy more IPv4 addresses does not conform to the intent of this policy. Further, if an organization, already has access to IPv4 resources of any kind, there is a strong presumption they don't need to access this pool.  

Thanks