Mike, Dude was doing fine on 0.25 IU
until he started to eat dry food.
It is encouraged that you try and wean him off the syringe, and I understand he prefers kibbles over wet food. Most of them do. [At this point I'm certain most of the kibbles are infused with cat crack or something that makes the cats addicted.] But as other members stated, in the US there are much better options available, such as Dr Elsey's - which you stated you already ordered/trying out with him hopefully by the time I'm posting this.
Purina DM is the devil. I'm not sure whether I posted this, I remember I wanted to and typed it up, but perhaps didn't send the comment - if I did, apologies for the repetition.
Mister's BG skyrockets on Purina DM. Let alone that, it's incredibly addictive - my other two cats wouldn't touch anything else anymore, hardly even their favourite wet food, which was never an issue prior to changing their cheap kibble to ProPlan. "Veterinary diets" are marketing campaigns and the practices that push those receive commissions from the big corporates [Purina, Hill's, Royal Canin] - my vet confirmed this. Doubt it would be any different in the US.
I have to agree with Wendy. In my opinion Dude is
a) either dropping too low in the PM cycle on 0.5 IU and bounces back high by the AM, or
b) he's giving you horrendously high numbers due to the dry food.
Or perhaps both of the above.
When you fed him only ±5g dry
prior to nadir/+6 he was still OK, but feeding him that junk and in higher amounts right before pre-shots is screwing with him.
LOL come on, man! We all wrong then, yeah?
Did you do the math? I hope you did, and it was on the callipers...

They are easy to use, once you have a starting point carefully measured. This is the only tricky part that takes time. You have to have a reference point, if you're lucky it ends in an even number e.g.
1 IU = 1,40 mm
You double-triple-quarduple check that value on many syringes randomly, at random places along them [
not only on the top 1 IU] to ensure validity and reliability. Once you have a starting point established, it's simple math from then on and the syringe markings can be completely ignored.
Dude was doing fantastic. Don't take that away from him with the dry food for your and his temporary comfort/convenience and with excuses of lack of ability to measure certain doses, because you're doing more damage to him on the long run.
You're provided with all the help and info now, that you were in so much need of at the beginning. Use it then. For the sake of your cat.
Edit: Should you change syringes to BD micro-fine, there is a printed dosing chart for that specific brand that allows you to dose even as little as 0.1 IU. That chart was made by the Germans, so you can be sure it's precise

I'm sure it's linked on FDMB somewhere, but if not, I'll copy it for you from my profile on the German forum.