It isn't that I think there there is no difference between .4u and .25u, its just that I think he has a sweet spot Im skipping over. Not to mention that I haven't had this type of issue in the last 5 years. Here is my source...or at least one of them.
Insulin glargine is a human insulin analog that has been designed to have low aqueous solubility at neutral pH. At pH 4, as in the LANTUS injection solution, it is completely soluble. After injection into the subcutaneous tissue, the acidic solution is neutralized, leading to formation of microprecipitates from which small amounts of insulin glargine are slowly released, resulting in a relatively constant concentration/time profile over 24 hours with no pronounced peak. This profile allows once-daily dosing as a patient’s basal insulin. In clinical studies, the glucose-lowering effect on a molar basis (i.e., when given at the same doses) of intravenous insulin glargine is approximately the same as human insulin. In euglycemic clamp studies in healthy subjects or in patients with type 1 diabetes, the onset of action of subcutaneous insulin glargine was slower than NPH human insulin. The effect profile of insulin glargine was relatively constant with no pronounced peak and the duration of its effect was prolonged compared to NPH human insulin. Figure 1 shows results from a study in patients with type 1 diabetes conducted for a maximum of 24 hours after the injection. The median time between injection and the end of pharmacological effect was 14.5 hours (range: 9.5 to 19.3 hours) for NPH human insulin, and 24 hours (range: 10.8 to >24.0 hours
https://www.accessdata.fda.gov/drugsatfda_docs/label/2007/021081s024lbl.pdf
This amongst other ncbi articles or Mayo Clinic pieces all refer to the maximum effect of Lantus being 24 hours. Typically ranging from 14-16 hours.
Coupled with my experience of having veterinarians telling me my cat was no longer diabetic and to literally STOP giving him insulin, only to watch his BGs rise to eventual hyperglycemia, I have a hard time believing anyone outside of myself or my experience. If it weren't for my hard headed nature and conviction my cat would have not been nearly as healthy as I have kept him for these last five years. Unfortunately every professional or anyone else that has intervened in his diabetes has only offered information that, had I taken at face value and applied, would have resulted in him being much less healthy and much less efficiently regulated.