There are no really good pharmacology explanations for being more hungry on reta than being on nothing for 2 months. The glucagon agonism could theoretically make you more hungry but I don't see how it could with the gip and glp-1 agonism at the same time. Maybe you have some weird receptors.
Realistically you are still on a microscopic dose. Despite people saying the effects kick in at a certain dose with reta, it is actually the only one that produces a lot of weight loss at low doses , nearly 9% at 1mg/week over a year. Everyone on this forum says it is less effective at reducing hunger than tirz, the weight loss results do not agree with this. Yes it probably makes you use an extra 100-200kcal day of extra energy at higher doses due to the glucagon agonism, but if people were really eating more on reta, they would not be losing as much weight. 100kcal/day is only about 4.7kg of fat over a year ( 365 x 100 / 7700kcal/kg of fat tissue ). Interesting that that alone would be enough to explain the extra weight loss compared to tirz.
Assuming you do not want to give up on it and go back to tirzepatide, you are actually already using the one reasonably safe strategy to increase doses rapidly, quite similar to what I did to go from 0 to 15 mg of tirzepatide in a month. 1 mg per day and keep going with that until hunger goes down or you start getting side effects, and if you get to a week then 1.5mg per day. Given absorption takes about a day, you are fairly unlikely to get severe side effects suddenly as it should only take a day or 2 to have blood levels drop back down to the level they were at before the most recent dose. And if you start getting side effects stop the increases and stabilise. The fact that you tolerated 10mg of tirzepatide makes it very likely you would tolerate a roughly equivalent dose of reta, which if I had to guess I would put at about 7-8mg, so I think in someone who has already shown they tolerate glp's ok increasing doses rapidly by low daily doses is safer than average. I would not recommend this to anyone who has not been on glp's before or if diabetic or with multiple medical issues. But it would save you weeks to months of being extra hungry while waiting for it to start working. I would be extremely surprised if you did not start feeling a lot less hungry once you got to a week of 1mg doses per day. And once you work out a dose you like you can space it out to higher doses less often so long as they add up to the same number of mg per week.