Mammut boot fitting issue

So got a pair of mammut mamook thermos, moderately used by the looks of them for an absolute steal. They are a half size bigger than my asolo hiking boots and the same size as my asolo plastics climbing boots. I read that the mammut a have a narrow fit as do the a solos I own. My first impression when trying these boots on was agreeable. They felt like a good fit, I could wiggle my tows slightly even with a heavy merino wool sock. But after walking just a mile in them on flat ground, I got some sweet blisters at the top of my heel, just below the Achilles. It didn't feel like I had a any heel lift. I was wearing medium weight merino wool socks and no liners. Suggestions? Can. These be stretched at all?? I'm new to the climbing game so I'm all ears

Did you play around with the lacing and ankle strap to make sure your heel is locked down? I recently bought a pair of these, and just love them! I've climbed in them 4 long days, with some pretty rugged approaches and have yet to get a hot spot anywhere. Fwiw, I do wear two socks - I have to with any hiking boot I have ever owned. My feet are very narrow. You could try a liner, but get a wool one. I find the synthetic liners to be abrasive. I use a very thin ski sock as a liner and a thick wool hiker over that. If you don't have the room, try two thin socks. Could be that they just don't fit your foot shape, or that they were broken in to someone else's foot.

So I think the heel cup is a little too short, that's short not shallow for my feet. After a week of playing with the boots the only way I could get them to feel good was giving my heels a quarter inch taller of a heel cup by cutting the back 1/3 of the insole out and thus lowering my heel. Anyone see a disadvantage to this??? Could that hurt the boots performance at all beyond maybe being a little colder?? Anyone one see other solutions?