Welcome Sabrina and Dale.
Lantus is a well researched, long acting insulin that has an admirable track record of getting cats into remission/diet controlled status. That said, the method of getting cats OTJ or tightly regulated is to follow the protocol that has been effective in getting cats into remission. If you look at the sticky note at the top of the board,
Lantus & Levemir: Tight Regulation Protocols, you will find the modified version of the protocol we use here along with the links to the full protocols.
Fundamentally, what these protocols require is aggressive home testing and using the data from your home testing to guide dosing decisions. You will need to routinely get pre-shot tests along with mid-cycle tests. Doses need to be held until reductions are earned or increases are indicated. Based on your spreadsheet, you aren't getting pre-shot tests on a regular basis. While dosing decisions are not based on the pre-shot number, you need this information in order to guarantee that it is safe to administer insulin. Likewise, without spot checks, you don't know either when the nadir is or whether a dose reduction has been earned. We are very numbers driven because we have found it is the best and safest way to get a cat either tightly regulated or into remission. While there is variability in how much each of us is able to test, you will find consistency with respect to our getting pre-shot and at least one spot check per cycle, if not more. Please feel free to open our spreadsheets to get an idea of the frequency with which people here test. Reading the protocol will help you to better understand our spreadsheets.
While food is important, feeding a low carb, canned food diet is more important than what the brand of food is. While I could manage to feed my cats the premlum foods, frankly, they don't like Wellness and prefer Fancy Feast. As long as they eat and are eating food that is less than 10% carb, we're all happy.