Try to change your mindset slightly.
If you get 5 doses out of your 5mg pen which give you 5 weeks of the effect you want it doesn't matter if you throw away some liquid at the end, you are still winning.
If 2.5mg lets to stick to your chosen calorie deficit, then stick with it until you need to increase.
Then consider 3.75mg and stick with that for a few weeks to see if the compounded increase gives you the effect you need.
I am 8 months on Mounjaro and still on 3.75mg. Some days or weeks the suppression effects are lower, but they are enough to keep me on track, then some days or weeks they come back strong, so I am glad I didn't react and increase too soon.
Getting the most out of the lower doses, if they let you stay in your calorie deficit, saves you money by not increasing too quickly to the more expensive pens.
Also have a look into and consider if you would take a 6th dose from a pen. So doses on days 0,7,14,21,28,35. It is obviously a risk as outside the 30 day limit by 5 days and something to research yourself. I feel it is low risk and have taken 6 doses from my last 6 pens, I would not take a 7th as too far beyond for me. I have seen on here some suppliers will question if you only order every 5-6 weeks so watch out for that too.