Don't forget a) the OP already said it won't mount the other way up and I have no reason to doubt that they tried, and b) that case seems to have a PSU shroud that extends above the bottom of the radiator so you need to factor in an extra 5cm or so to account for the awkward bends that would be required. Possibly rotating the block so the hoses come out of the bottom would give enough slack, but just based on the pictures it doesn't look to me like there's any chance of it reaching.
In general most AIOs seem to have hoses that are around 35cm long, and given that on an ATX board it's about 30cm from CPU socket to bottom right corner there's not usually a lot of choice in which way up it goes - once you take routing it round other hardware into account hoses up is more often than not the only option.
Annoyingly AIO spec sheets (or even reviews) rarely mention the hose length so there's really no way of knowing until you try, but the Arctic Liquid Freezer II has 45cm hoses which explains why yours fits the other way up. (I'm guessing the OP has an ML360R which, from the few reviews that seems to think it worth mentioning, is on the shorter end but I can't find an actual figure anywhere.)
All that said, even if it's not ideal it's not going to be catastrophic if you can't mount everything in the optimal way. The pump might make a bit of noise when you first power it up when it's been idle for several days and cooling may lose a percentage point or two efficiency, but if your particular hardware combination means you can't put things in the perfect position it's not the end of the world - as long as most of the water in the system is above the pump it's going to be juuuust fine. I occasionally consider remounting mine so it's on the top of the case but it's honestly more trouble than it's worth - I never even get close to the thermal limit on anything, and the four miles of RGB and fan cables were a nightmare to manage and I do not want to do it again if I don't have to!
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