you've got a variety of factors that all play together - you've got a dose, the carb content of the food you give, the volume and/or timing of feeding (when in relationship to the Lantus dose), and the cat's body. Each of those things can raise or lower the blood sugar.
what we try to do is to control factors that we can, so that we can see what is doing what.
when the cat's food carbs drop dramatically, we know that can result in needing a lot less insulin. we've had people do little experiments with their cats where even as few as 3 or 4 kibbles will make their BGs rise and keep them there for another day or so. depends on how carb sensitive a particular cat is. that varies from cat to cat.
now that the dry food has gone away, if you're going to stick to low carb canned food only now, he will need less insulin. we'd rather have him be a little high for a day or so than have him go too low from too much insulin.
let me be the first to say that in spite of what liz is saying, i don't know all. :lol: i know some - from what i learned with punkin and what i've learned from other kitties here. there are plenty of people who know more than me - i'm not the most experienced person. so you can consider my advice, but the best thing is going to be if you listen to everyone that posts, and as you can, read up on feline diabetes. that's why we require that advice be given in posts so that they can be peer reviewed. it improves the quality of the advice you get and we all learn from it.
the learning curve is so steep at the beginning that we try to just tell new folks what we'd suggest they do, while explaining the why of it so that they can learn. it takes a while before anyone sees it on their own. i wrote the post on bouncing and admitted there that it literally took me 6 months to be able to spot a bounce. ohmygod_smile you think you should get it sooner, but i didn't.
Kim had an awesome explanation above. Many people here work. one of the best tools for a working person is a timed autofeeder. i was home for the first year that punkin was diabetic, then went back to work and the autofeeder gave me incredible peace of mind. it is absolutely possible to work around work. Prince is diabetic whether you're gone or not, so learning how to read what he's done before so that you can predict what might be coming in the next 12 hours becomes a huge asset in managing him safely. i'm going to guess that you'd also like a life still, and would like to be able to leave home for more than an hour at a time. you can absolutely learn ways to keep him safe while you are gone. we don't all sit and watch our cats all day!
given all of that, the choices are always yours. we'll try to explain the reasons behind what we suggest - he's your kitty, so you always are the one making the final decisions. and no one minds you asking yet more questions - that's the only way you gain confidence in understanding your own decisions. we expect it - we were in your shoes at one point too.
so ask away.
I married a Canadian and lured him to the US 
We want the best thing for our babies NOW!