In the first image it kind of looks like the stick is not fully pressed into the slot because the ram radiators are blocked by the hdd bracket by the corner, and you could install the ram with radiators if you detached the hdd bracket, installed the ram and then reattached the bracket since the ram radiators have cut corners there. Really weird shotSome RAM compatibility anecdotes: I first tried the Team Dark Pro 3200 MHz CL14 modules which are 45 mm tall, but the heat spreader design means it doesn't conflict with the bracket. And even if it didn't fit, I had the option to unscrew the plastic piece at the top, which is separate from the actual aluminum heat spreader and reduces the height by a good amount. Unfortunately even with Samsung B-die memory, it failed to boot on my motherboard. I updated the BIOS and finally got it to boot, but couldn't overclock to 3200 MHz. So I downgraded the UEFI and switched out for G.Skill Flare X 3200 MHz CL14, very pricey but the guaranteed compatibility was nice and overclocking was ridiculously easy.
Even though the Flare X is only 40 mm tall, the design of the heat spreader means the Sentry's HDD bracket will rest on top of the RAM module. There isn't any pressure or tight fit, but there isn't complete clearance like there was with the Vengeance LPX or Team Dark Pro. The G.Skill Flare X comes with temperature sensors and temps don't seem to be affected, and 30 minutes in RealBench (8GB allocated) went fine, and the faster RAM gave me a couple more points in Cinebench R15. I was still able to mount my 2.5" SSDs without any problems. Some pictures for anyone looking into these modules for use in the Sentry:
Also note that there should be short countersunk screws in the package for the purpose of mounting that hdd bracket so the won't stand out this much and will let you install second 2.5" drive into that bracket.